[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  -s ours

Change-Id: Ied0f3936cbc6370ed53e989c56c23a88a417658d