Bump Security Patch Level to 2018-04-01

Implemented patches
===================
CVE-2017-13274  A-71360761      High            Change 211306
CVE-2017-13279  A-68399439      High            Change 211334
CVE-2017-13267  A-69479009      Critical        Change 211337
CVE-2017-13290  A-69384124      High            Change 211340
CVE-2017-13295  A-62537081      Moderate        Change 211342
CVE-2017-13298  A-72117051      High            Change 211346

Skipped patches
===============
CVE-2017-13277  A-72165027      Critical        No libhevc
CVE-2017-13280  A-71361451      High            No fw/ex/framesequence
CVE-2017-13284  A-70808273      Critical        No ext/bt/bluedroid/osi
CVE-2017-13285  A-69177126      High            Can't fork svox due to DMCA
CVE-2017-13289  A-70398564      High            No RttManager
CVE-2017-13296  A-70897454      High            No libavc
CVE-2017-13297  A-71766721      High            No libhevc
CVE-2017-13299  A-70897394      High            No libavc
CVE-2017-13300  A-71567394*     High            Not publicly available
CVE-2017-13278  A-70546581      High            Not applicable without major changes
CVE-2017-13294  A-71814449 [1]  Moderate        Not applicable (Pixel bulletin)
CVE-2017-13294  A-71814449 [2]  Moderate        Not applicable (Pixel bulletin)
CVE-2017-13287  A-71714464      High            No VerifyCredentialResponse
CVE-2017-13276  A-70637599      Critical        Not applicable without major changes

Reference Version: 6.0

Change-Id: I0db37cce05279144562ff116334876cae8024a70