gbp-clone: support repo URLs like "host:repo.git"

Previously, gbp didn't correctly parse this kind of URL and clone
failed.

Signed-off-by: Guan Junchun <junchunx.guan@intel.com>
Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>
gbp-clone: support cloning to a specific directory

Closes: #725666

Signed-off-by: Guan Junchun <junchunx.guan@intel.com>
Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>