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: I345eaaee269f6443527f45a9be7e4ee47f6b2b39
(cherry picked from commit 68c5a679)