fs_mgr: Set the 'partition.*.verified' property for verified partitions.

This modifies fs_mgr to set the partition.*.verified properties.
Each of these should be used as a weak indicator that a given partition
is verified. For instance, if the 'partition.system.verified' property
is set to '1', this could indicate that the system partition is verified
and therefore should not be modified by, e.g., adb sync.

Note that these properties can be mutated by the system, and so
should not be used as the basis for security decisions.

Change-Id: I27215a3d3628a1b1e184df9eaad90541b9d8b841