Make storage dirs remount fork() safe

Also, use the pids provided by system server to remount all existing
processes, so we don't need to do the heavy and unreliable scanning in
/proc anymore.

Bug: 149548518
Test: atest AdoptableHostTest
Change-Id: Ifb5b79a3bc5438f36e0d61ec8aec96bdbc60ca13
7 files changed