Speed-up builds by changing RPM compression method and level

Result               BEFORE              AFTER
writting src rpm     374s                  80s   gain x4
wrtting binary rpm   1821                  170s gain x10

BUG=XWALK-2571
Signed-off-by: Stephane Desneux <stephane.desneux@open.eurogiciel.org>
Merge pull request #2455 from eurogiciel-oss/build_speedup

Speed-up builds by changing RPM compression method and level