debian packaging: introduce -common subpackage

debian packaging: introduce -common subpackage

Split the git-buildpackage into git-buildpackage and
git-buildpackage-common. Now there are three binary packages:
- git-buildpackage-common contains the common code for Deb and RPM tools
- git-buildpackage contains the Debian-specific modules/tools
- git-buildpackage-rpm contains the RPM-specific modules/tools

After this change the Debian packaging resembles the RPM side packaging.

Signed-off-by: Zhang Qiang <qiang.z.zhang@intel.com>
Signed-off-by: Ed Bartosh <eduard.bartosh@intel.com>
Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>