Refactor python to rpm names conversion

Split convert_names_to_rpm method of py2rpm helper into two
higher-level methods:
- names_to_rpm_names, which returns a dict name -> rpm_name, which
  allows to get rid of unsafe zip(...) usage -- reqs and rpm names will
  never be out of sync again;
- names_to_rpm_requires, which returns list of RPM-styled requirements
  with versions for usage in specfile rendering.

Change-Id: I71faa244ae53bd2cefe872d0bf595c9aa4049812
Merge "Refactor python to rpm names conversion"