Clarify tempest-full job description

tempest-full is py2 job and only supported until
stable/train as Tempest/devstack or any other OpenStack
service (except swift) are python3-only from ussuri onwards.

This job can be run on ussuri gate onwards for py2.7 test coverage
but it needs to be overridden with stable/train or any stable branch
less than stable/train. Supported nodeset for overridden stable
will be handled by branched devstack.

Also replace few jobs parent from tempest-full to tempest-full-py3.

Change-Id: Icbd0ed88736f0ac746cd1fe20eb9b1f7d739f6bd
1 file changed