lowmemorykiller was not taking into account unevictable pages when
deciding what level to kill. If significant amounts of memory were
pinned, this caused lowmemorykiller to effectively stop at a much higher
level than it should.
bug 31255977
Change-Id: I763ecbfef8c56d65bb8f6147ae810692bd81b6e2
Signed-off-by: Tim Murray <timmurray@google.com>