Only launch in-tree zuul jobs when necessary
Only launch in-tree zuul jobs when necessary

Adding 'irrelevant-files' attribute for the in-tree zuul jobs to avoid
unnecessary launching. Also add new abstract jobs to hold common
attributes among similar jobs.

Change-Id: I047412f7fee494e7638f9bdabe0c022619e5fb33
Signed-off-by: Zhao Chao <abb6a2f7e4fabebf6d227485f53d7acf834f1da2@gmail.com>

openstack/trove,openstack/trove