Relocate branch conditional for tempest-full job

This condition was added to openstack-zuul-jobs in [1], but it created
bug #1739829 as a side effect. While addressing the issue [2] it was
noticed  that conditional could be located in the tempest repo itself,
so this patch aims at cleaning things up a bit and reduce the moving
parts.

[1] I799ea86f3c445bb067950a8cbc237999d621e3a9
[2] I5d34e5b983b720dc1913d00ccc1a16d81a040d49
Needed-by: Ibfbc925af6eb274ced53312301b1733136ba4455
Partial-bug: #1739829

Change-Id: I8e0aa11cd2d92d5d6f5e9147a407374948920e7f
1 file changed