Mount pstore filesystem while in recovery

* pstore filesystem is evolution of ram_console and contains
  kmsg from previous boot (previously in /proc/last_kmsg).
* Lollipop init.rc does this. If device doesn't have
  pstore fs, it will simply be ignored

Change-Id: Id3bf8763ccde54f87fde5cdf2db511649c376aa4
Signed-off-by: Vojtech Bocek <vbocek@gmail.com>