LU-9870 build: handle SNMP missing on build box

LU-9870 build: handle SNMP missing on build box

Currently the lustre spec file doesn't handle the case when SNMP
is missing. So even if the user does configure --disable-snmp our
rpm build process will ignore this and fail to build rpms. Pass
to the rpm build process the missing SNMP case.

Lustre-commit: 574451a4402df65d26d7af96d94a7bf0875c86af
Lustre-change: https://review.whamcloud.com/28494

Test-Parameters: trivial

Change-Id: Ia6dcfd31b50f4f67afe7a4545fe417c32df6e559
Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Minh Diep <minh.diep@intel.com>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Reviewed-on: https://review.whamcloud.com/28987
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>