Add statement explaining "tips" job configuration
The configuration of the periodic "tips" jobs in .zuul.yaml may
be confusing, particularly after a stable branch is cut.   Add a
comment explaining what we're doing and why to reduce confusion.
- glance_store-dsvm-functional-swift
periodic:
jobs:
+ # NOTE(rosmaita): we only want the "tips" jobs to be run against
+ # master, hence the 'branches' qualifiers below. Without them, when
+ # a stable branch is cut, the tests would be run against the stable
+ # branch as well, which is pointless because these libraries are
+ # frozen (more or less) in the stable branches.
+ #
+ # The "tips" jobs can be removed from the stable branch .zuul.yaml
+ # files if someone is so inclined, but that would require manual
+ # maintenance, so we do not do it by default. Another option is
+ # to define these jobs in the openstack-infra/project-config repo.
+ # That would make us less agile in adjusting these tests, so we
+ # aren't doing that either.
- glance_store-tox-py27-cinder-tips:
branches: master
- glance_store-tox-py35-cinder-tips:
