LU-5919 build: Make "make rpms" use "make srpm" output

LU-5919 build: Make "make rpms" use "make srpm" output

We rework the rpms and srpm Make targets.  The srpm
target generates the source rpm package much as it did
before, but it puts the results in a known temporary
rpm build tree.  This allows the "make rpms" target to
simply depend on the srpm target, and then build the
binary rpms from the source rpm.

Previously the rpm target _also_ generated a source rpm
package, which could be redudant, and failed to verify that
the source rpm package was itself buildable.

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Signed-off-by: Christopher J. Morrone <morrone2@llnl.gov>
Change-Id: I9b2e83e000aca62b5d4841e2ebe9e91fa1db300f
Reviewed-on: http://review.whamcloud.com/12961
Tested-by: Jenkins
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>