applypatch: Support flash mode.

We may carry a full copy of recovery image in the /system, and use
/system/bin/install-recovery.sh to install the recovery. This CL adds
support to flash the recovery partition with the given image.

Bug: 22641135
Change-Id: I7a275b62fdd1bf41f97f6aab62d0200f7dae5aa1
(cherry picked from commit 68c5a679)