The main goal of this patch is to keep all DEBUG logs and packet logger enabled
without exploding disk usage.
This is done by keeping the last 16 MB (by default) of debugging information in
a RAM buffer, and to emit it to an SQLite DB upon RTMIN signal or in case of
warning and more severe log.

Implementation is also cleaned up for better integration within a framework
or if run standalone. NEO logger is now a direct child of root handler.
Only warnings and more severe logs are forwarded to root handler.

A new script 'neolog' is added to pretty-print the contents of the SQLite log.

In unit tests, logging events are not buffered but emitted immediately.
When a test passes, payloads of all exchanged packets are discarded to reduce
disk usage on test bots.

This slows down performance tests by about 15 % because even if nothing is
written to disk, debug and packet log records are now always rendered.

sed is your friend.
Also, factorise setUp definition.
Also, use "super" to call methods on superclasses.

Preserve AskPrimary/AnswerPrimary for neoctl/neoadmin exchange only.
Fixes several race conditions during election.

Otherwise, in the case of an unexpected packet, an incorrect message id
would be used.
Also, refuse setting a None peer_id on connection.

This includes an API change of Node.isIdentified, which now tells whether
identification packets have been exchanged or not.
All handlers must be updated to implement '_acceptIdentification' instead of
overriding EventHandler.acceptIdentification: this patch only does it for
StorageOperationHandler

Roughly once every 40 tries on ClusterTests.testElectionWithManyMasters I
get a "port already in use" because runner assigned two master to the same
port.

MasterHandler contains only server-side handlers.

Also, factorise code to be executed when connection is established.