Added repo cherry-pick command

It is undesired to have the same Change-Id:-line for two separate
commits, and when cherry-picking, the user must manually change it.

If this is not done, bad things may happen (such as when the user
is uploading the cherry-picked commit to Gerrit, it will instead
see it as a new patch-set for the original change, or worse).

repo cherry-pick works the same was as git cherry-pick, except that
it replaces the Change-Id with a new one and adds a reference
back to the commit from where it was picked.

On failures (when git can not successfully apply the cherry-picked
commit), instructions will be written to the user.

Change-Id: I5a38b89839f91848fad43386d43cae2f6cdabf83
1 file changed