Add a e2e for self-ping, with a single channel resource

Add a simple e2e test that joins a channel with xep0106-encoded name

Reset the preferred private JID when all resources leave a room

For example if we are talking in private with nick Joe from
room #foo, and then we leave that room, we start receiving Joe’s
message from the server-wide JID

e2e tests included!!!

Add some e2e tests to check that private messages come from the right JIDs

Add a basic e2e test for channel and private messages

Associate a bridge with a bare JID instead of a full JID

ref #2556

Test the execution of the hello command

e2e: possibility to extract a value from a stanza and reuse it in send_stanza

Change the name of the DB in the e2e tests

Include the Configure ad-hoc command on biboumi's JID  for fixed_irc_server

Because a jid like “freenode.example.org” is both the JID for the configured
IRC server, and biboumi’s JID.

fix #3175

Trivial cleanup

Add e2e tests for the ad-hoc listing on the server jid

Remove a forgotten comment

[ci skip]

Test the the virtual channel

tests: Split the connection sequence into two

We can now insert steps between the two parts

Remove an unused variable

Add a basic fixed_server e2e scenario

Each e2e scenario can provide its own config name

Write irc output into a file

Debug and exit if IRC server startup fails