Bug 974270 - Re-enable the majority of datastore tests on b2g; r=khuey

I have no idea what has fixed these tests, but the try server says
they are fixed.  We always suspected that this is caused by a bug
in the mozapps code, and there has been some development there, and
elsewhere.

--HG--
extra : rebase_source : 2122a1016c3505b833d11b49cf63f79f117792e5