Low: build: add conditional build flags to %configure in RPM spec

Make sure that the conditional build flags are honored by
%configure. Otherwise, if one were to build an RPM, for example,
"--without snmp" but had the Net-SNMP headers installed, crm_mon would
still be linked against Net-SNMP.

Mercurial revision: 147f9e0082b0bea0932f431571a8fd6764e761b8