Allow to assign a default channel on @job functions

[guewen]

When the @job is registered and created in the database, it lookups its
channel and creates it if it don't exist yet.

Allows to do:

@job(default_channel='root.channel.subchannel')
def a_task(session, arg):
    pass

Also add tests on jobs and channels models

[guewen]

I thought it was merged in the jobrunner branch but it appears it wasn't. Thus I propose it again on the 8.0 branch.

[coveralls]

Coverage increased (+0.56%) to 75.14% when pulling b299b6b on guewen:default-channels-on-jobs into aa5cf84 on OCA:8.0.

[sbidoul]

It must have been lost in the last rebase, sorry.

👍

[guewen]

It must have been lost in the last rebase, sorry.

No problem :-)

[lmignon]

👍

[yvaucher]

👍