[Omaha] Move most functionality to OmahaBase, add JobService
* Move almost all pipeline functionality from OmahaClient to OmahaBase.
Most of the code changes are strictly code moves, except for a change
to make it easier to change what Delegate is being used.
* Add a JobScheduler version of the OmahaClient IntentService called
OmahaClientJobService. OmahaClient can't be renamed because we may
potentially have outstanding alarms on the system that reference it.
* Make OmahaClient be the IntentService that is triggered on Android L
and lower, and OmahaClientJobScheduler be triggered on M and higher.
BUG=
680817
Review-Url:
https://codereview.chromium.org/2664253005
Cr-Commit-Position: refs/heads/master@{#453504}
Committed:
https://chromium.googlesource.com/chromium/src/+/272eb7b955d8008142f9fd6615cea25161f684ac