hammerhead: Better mount options to improve performance

Change-Id: I18f7165c2ff8547b7968d946336d948fe30522b1
Signed-off-by: Rob Beane <robbeane@gmail.com>
hammerhead: Disable secure discard for now
 * Secure discard is causing wipes to take insane amounts of time.
 * Enable this workaround until the problem is sorted.

Change-Id: If9bbb27fd5476a160e9d7e8b29ab20a851410ff7