create-pull-request: Fix error on 2.0 versions of git
On 2.0 versions of git, the create-pull-request script exits with the
warning "No match for commit... Are you sure you pushed 'HEAD' there?".
This is due to a change in behavior where git used to guess the branch
you meant, but no longer does. See the thread at
http://www.spinics.net/lists/git/msg233050.html for more information.
To accommodate the new behavior, if the COMMIT_ID is set to the default
of "HEAD", make it point explicitly to $BRANCH instead.
Signed-off-by: Ben Shelton <ben.shelton@ni.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
