LU-5090 build: restore enable-mpitest option

LU-5090 build: restore enable-mpitest option

Originally the enable-mpitests configure option was deeply
embedded in the liblustre configuration test. With the
removal of liblibustre this option got accidentally removed.
This patch restores this option.

Change-Id: I92ab1d3f187f579dca4bb6825a5bf1e80dbbee06
Signed-off-by: James Simmons <uja.ornl@gmail.com>
Reviewed-on: http://review.whamcloud.com/10384
Reviewed-by: Brian J. Murrell <brian.murrell@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Jenkins
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>