rpm: add version parsing functions to pkg policy

rpm: add version parsing functions to pkg policy

Adds functions for version string generation and parsing. These are
intended for parsing version strings taken e.g. from rpm filename or
changelogs.

Also, take these new version parsing functions into use in the rpm gbp
scripts.

Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>
Signed-off-by: Ed Bartosh <eduard.bartosh@intel.com>
Conflicts:
	gbp/rpm/policy.py
	gbp/scripts/buildpackage_rpm.py
	gbp/scripts/import_orig_rpm.py
	gbp/scripts/pq_rpm.py