Add fs_mgr option to enable/disable quotas.

To support upcoming disk usage calculation optimizations, this change
adds a new 'quota' mount flag.  As part of mounting an ext4 device,
we now enable/disable the quota feature using tune2fs to match the
requested value in the fstab.

When changing the quota status, we force a fsck pass on the device
before actually mounting it to prime the quota data structures which
are stored in hidden inodes.

Changing quota state and priming the data structures needs to happen
before we actually mount the device, so fs_mgr is the best place to
place this logic.

Test: builds, boots, enables and disables quota
Bug: 27948817
Change-Id: I7ccbf97cbc4a679bdd7a31a77be4b99aa9a88e66