[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

Change-Id: I7040b190348f3264f16fb0564e5b982a085f5c11