pivotaltracker: Implement common.NextRelease

And make sure release start works when the Pivotal Tracker module is activated.

Change-Id: e3ad0cee65
Story-Id: SF-101
wip [ci skip]

Change-Id: 68c21a84fa
wip [ci skip]

Change-Id: 7d934b2280
wip [ci skip]

Change-Id: 82866c0f2f
wip [ci skip]

Change-Id: 2fe92cf0ee
wip [ci skip]

Change-Id: ff79fbeea9
wip [ci skip]

Change-Id: e85e17606f
wip [ci skip]

Change-Id: 216e9ab4d0