We must be sure that people won't change this code, because we need to
care about backward compatibilty.

MARKER is not required, it just polutes the code.

And should not prevent a bad usage of the library.

There is no time yet for such changes in libnetworkcache.

Sorry, it should not be commited in the previous commit.

In this case, super does not beahvior as expected, so it is better to
call the init method directly.

Actually, the NetworkcacheClient must be able to fetch the
certificate files under a HTTPS server.

So, these classes and methods are going to be used to setup the
environment to test this feature.

Once the tests are growing up, I decided to organize it in a clean way.

test_libnetworkcache  - tests to NetworkcacheClient class
test_signature        - tests to signature script
libnetworkcachemixin  - an util module with all the code which is
                        required to setup the test environment

NOTE: THERE IS NO CODE CHANGE.

This test must prove that when the signature_certificate_file_list
has a path to the file system and urls, the file system path has high
priority over the urls.

To download contents in a correct way, it must use the
libnetworkcache.

This file must provide all the utils function, to avoid duplicating
code.

This file must provide all the utils function, to avoid duplicating
code.

This library aims to handle all the possibles way to do a GET to an http
server.

So, it must contains all the code related to HTTP calls to avoid to
polute the NetworkcacheClient class with this kind of code.

The NetworkcacheClient should use this library to download any kind of
file which is necessary.

Using this library NetworkcacheClient must be able to:
 - download a file under HTTP without authentication
 - download a file under HTTP with basic authentication
 - download a file under HTTPS CA (Certificate Authority)
 - download a file under HTTPS CA with basic authentication
 - download a file under HTTPS with Certification Authentication

So currently, this library only provides a way to:
  - download a file under HTTPS CA (Certificate Authority)
  - download a file under HTTPS CA with basic authentication

(work in progress)

Well, _MARKER is used to backward compatibility and to raise an error
which if the networkcache server is not consistenty.

Without _MARKER there is not way to make these conditions.

A simple object of NetworkcacheClient class is already instantiated by
setUp method.

Following the previous commit, _MARKER is not required anymore.

Well, before this change the signature_certificate_file_list worked
only with filesystem paths.
 - i.e ['/home/user/public.pem']

Now it is possible to define urls as well.
 - i.e ['http://example.com/public.pem']

The url content will be downloaded to a temporary file before the
verification and automatically removed after.

The filesystem paths has higher priority than url, it is checked first.
If it does not find any valid certificate, then it will try
to download the certificates from the url provided.

This is the first version has only basic tests.

The new test class aims to test the behavior of NetworkcacheClient
class. And it is forbidden to change any behavior of
NetworkcacheClient without writting/editing the tests.

NOTE: still WIP...

Now the mixin class is able to create the files which are required to
add the signature, it will be usefull for TestNetworkcacheClient.

Well, the LibNetworkCacheMixin has been created to avoid any kind of
code duplication inside of this test suite.

This mixin class is gonna be used by TestNetworkCacheClient.

Some variables have been renamed for a better understanding, but the
behavior of the code still the same.

It is not recommanded to use httplib directly, we should better
use urllib2, then this library will use httplib. This solve
issues with libnetworkcache when we try to use it behind an
http proxy.

Actually, the user can configure the buildout.cfg and set multiples
certificates files.

It means that libnetworkcache must be able to check if the signature
which comes from shadir is trustable or not, based on these certificates.

A given signature can not appear twice in the same directory-key, if it
happens a DiretoryNotFound error must be raised.

Renamed signature_public_file to signature_certificate_file, because the
name is cleaner once the content of the file is a X509 certificate
file. It is also known as Public Key Certificate.

Renamed signature_private_file to signature_private_key_file, because
the is is cleaner once the content of the file is a private RSA key.

Actually, the slapos.libnetworkcache has new dependeincies because
M2Cryto is required to handle the signatures inside NetworkcacheClient class
and the argparse is required by signature.py script.

Now it is possible to create the signature files easily using the
command generate-signature-key with the correct arguments.

The command generate-signature-key works without any argument as well.

To check the arguments you must run with the parameter --help/-h.

It'll generate two file, one is a private key and the other is a
X509 certificate file.

Those files must be used by networkcache to play with signature.

The private key is required to sign the message before uploading it to
shadir. And the certification file is required to verify the signature.

M2Crypto is required to create the signature string and verify if it is
valid or not.

The signature private file is not required to verify the signature it is
only used to create the signature string.

The signature verification requires only the public file...

We should not send the signature in the property dict. Otherwise,
the validation of json schema will fail.