Build - repopick: skip a cherry pick if its already been merged

* override this behavior with the -f argument

Change-Id: I76db237f94eda6830d242e8a68a0b454e49d37d4
Signed-off-by: STELIX <ssspinni@gmail.com>
Build - RepoPick : Add support for git pull

Allow user to git pull patchsets and dependencies.
(cherry picked from commit df646304bdcef329e3fe7c12b68107de1f4cd42a)

Change-Id: Iec740f938e5fcb4184690fdc799f80a2b496bf50
Signed-off-by: STELIX <ssspinni@gmail.com>