Avoid deadlock when FSTRIM requested at boot.

When PackageManager decides that FSTRIM is required at boot, we
can end up in deadlock.  Work around this for now by kicking the
requested FSTRIM can down the road for a few seconds until we're
connected to vold.

Bug: 20228019
Change-Id: I47e422e618d99e59aed8a8b79227821a3012eb9f