RPM builds should be using Mock

The Debian package builds are using `pbuilder` to ensure clean and sane package builds, why don't the RPM package builds for Fedora, RHEL/CentOS, and openSUSE use Mock?

Mock supports the wide variety of RPM Linux distributions (Fedora, CentOS/RHEL, openSUSE Leap, openSUSE Tumbleweed) and is generally the preferred way to do clean, consistent, and reproducible package builds.

Is there something stopping us from using it for Ceph?