script/build-with-container: add --current-branch cli option

script/build-with-container: add --current-branch cli option

Add a new --current-branch argument that lets the user supply a name for
the current branch. This allows the automatic tag generation to avoid
calling git - something useful if the tree is not using a git checkout
(like a tarball). It also allows you to pull a temporary branch in git
but ignore it and act like the temporary branch is the base branch.

Signed-off-by: John Mulligan <jmulligan@redhat.com>
(cherry picked from commit c1713c5bc37b7e31bd84555066c06a72bb0f025b)