Build rpm_*_probes only if RPM library was found
Build rpm_*_probes only if RPM library was found

On some systems, eg. Debian, RPM is not present and dpkginfo_probe
is used for similar queries instead. Therefore attempt to build rpm
should be made only if rpm is present.

redhatrises/openscap,OpenSCAP/openscap,OpenSCAP/openscap,mpreisler/openscap,jan-cerny/openscap,mpreisler/openscap,mpreisler/openscap,mpreisler/openscap,OpenSCAP/openscap,redhatrises/openscap,redhatrises/openscap,OpenSCAP/openscap,mpreisler/openscap,redhatrises/openscap,jan-cerny/openscap,jan-cerny/openscap,jan-cerny/openscap,jan-cerny/openscap,OpenSCAP/openscap,mpreisler/openscap,redhatrises/openscap,OpenSCAP/openscap,jan-cerny/openscap,redhatrises/openscap