fs_mgr: update block device reference in verity metadata

The dm-verity metadata contains the block device path that is given to
the dm-android-verity driver.  If the device is using slot A/B, this
path is missing the slot suffix.

This patch makes fs_mgr replace all the block device path reference
with the one including the active slot suffix.

Change-Id: Ib624d0d18b12a8a287cac7f15605a2e0fb7c97c6
Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>