Add Change Owner group to documentation

Gerrit would not allow assignment of the Change Owner group using git push
because this group isn't written to the groups file by default.  Adding the
group to the documentation will hopefully help users figure out how to
make it work.

Bug: issue 2388
Change-Id: Ib57b306a749bdf2817cd9c2e47a824636945b6bc
Cleanup test of ScheduleConfig

Asserting not equals to missing doesn't sufficiently test the
value was parsed properly for a non-standard key. Instead check
for real values.

Replace the hacky MessagseFormat string parsing of Config with
API setters. The Config class is already well tested in JGit.
There is no need to obfuscate this code to "verify" again the
Config object can read from a string.

Change-Id: I60cbf6dae9621fe7a7d7a10c5db87a39d3b57aac
Downgrade JUnit to 4.10

The index tests for gerrit-review backend use some of the basic
testing library in Gerrit but are currently unable to upgrade to
JUnit 4.11.

Change-Id: I4359067acf354a37c810559db0ceacd45cc791ff
Make mime-utils and gwtexpui available for plugin build

Change-Id: Iecb21e6b5cb2522b36a4644abc6eabe3cea9bdd8
Merge changes I4359067a,I60cbf6da

* changes:
  Downgrade JUnit to 4.10
  Cleanup test of ScheduleConfig
Merge "Add Change Owner group to documentation"