Changes are from slapos.git repository.

  Unfortunally exising keys from open build service uses 1028-bit keys and debian 9 seems not reconize is as
  security enough, so on debian 9, we allow insecure repositories to allow re6st-node package be installed.

  This change can be re-worked in order to make the repository valid again.

  Grandenet is only a re6stnet service of VIFIB

Since buildout 2 no longer supports using multiple versions of Python
in a single buildout, we're now forced to use slapos.rebootstrap.

By adding Host: HTTP/1.1 header and checking the response the test
asserts, that server is able to serve on any hostname, which is
configured to server's IP address.

Note: skipped, as SSL is not fully configured on the server.

By adding Host: HTTP/1.1 header and checking the response the test
asserts, that server is able to serve on any hostname, which is
configured to server's IP address.

Do not redirect during request, just assert that redirection is
correctly returned form the server.

Keep test name generic and set to reasonable build time: 3h

Those tests are used by deploy-test ERP5TestNode testsuite.

By using separated frontend/backend requests and firewall configuration
allow to access ERP5 on public IPv4 of host on https port 443 and http
port 80.

In order to being able play with generated image many times avoid
needless writes there by using qemu -snapshot switch.

Registered ipcm variable can be checked against
stat.exists in order to assert existence of ipcm

I found that include paths of slapos package's perl were wrong (i.e. `/usr/src/packages/BUILD/SLAPOS/build` should be removed).

```
~> /opt/slapos/parts/perl/bin/perl -e 'print @INC,"\n"'
/usr/src/packages/BUILD/slapos/build/opt/slapos/parts/site_perl/lib/site_perl/5.20.2/x86_64-linux-thread-multi/usr/src/packages/BUILD/slapos/build/opt/slapos/parts/site_perl/lib/site_perl/5.20.2/usr/src/packages/BUILD/slapos/build/opt/slapos/parts/perl/lib/5.20.2/x86_64-linux-thread-multi/usr/src/packages/BUILD/slapos/build/opt/slapos/parts/perl/lib/5.20.2.
```

I think that this MR fixes this issue but not so sure. Can you please verify it ?

/cc @alain.takoudjou @rafael 

/reviewed-on !23

because for Debian, 0.479+slapos.gfd8673b is newer than 0.479+slapos2.g12d4231