update-patches: ignore git submodule changes
update-patches: ignore git submodule changes

Prior to this change, rdopkg would create patch files that included Git
submodule changes. During the RPM's "prep" stage, /usr/bin/patch did not
understand what to do with these, and would fail with an error.

With this change, rdopkg will create an empty .patch file instead.
/usr/bin/patch is able to process this successfully.

This doesn't make rdopkg aware of code changes *within* Git submodules,
but at least it will no longer construct unusable patch files when a
submodule does change.

djipko/rdopkg,redhat-openstack/rdopkg,hguemar/rdopkg,djipko/rdopkg,openstack-packages/rdopkg,openstack-packages/rdopkg,Akasurde/rdopkg,Akasurde/rdopkg,hguemar/rdopkg,redhat-openstack/rdopkg