[DO NOT MERGE] Update Security String to 2017-04-01 for mnc-dev am: 06a57496e6 am: a3e5f184eb am: 775af5ae5b am: 6ebebd3ee3  -s ours am: 8dd075b1c0 am: 89005ae01c
am: dc8df2ef3d

Change-Id: Ib2091b976928701ab6c8c3e5195c61546a6f41dc