Freezer: fix exception when parsing /proc/locks

The original code is based on /proc/locks manpage. Unfortunately, that
manpage is never correctly updated to include the new field for blocked
locks. The new code detects the extra field. As StringTokenizer is too
heavy, ProcFileReader is used for better performance.

Bug: 194756340
Test: FrameworksUtilTests com.android.internal.util.ProcFileReaderTest
Test: FrameworksCoreTests com.android.internal.os.ProcLocksReaderTest
Test: No /proc/locks parsing exception with blocked locks
Change-Id: I4c9763f9d3091f7d84d2e4b672d7e5cb78b33f59