rpm: add rpm-build to SUSE-specific make check deps

rpm: add rpm-build to SUSE-specific make check deps

The binary /usr/bin/rpmspec was recently moved to rpm-build, breaking
install-deps.sh on openSUSE Tumbleweed. The package is not strictly
needed for SLE-15-SP* and openSUSE Leap 15.*, but it doesn't hurt to
have it, and will future-proof these distros from this regression.

Putting the dependency in the spec file does not address the issue,
because /usr/bin/rpmspec must be available before install-deps.sh runs it to
determine the dependencies, but it's nice to have it explicitly listed there,
since it *is* a dependency of "make check" on SUSE distros.

SUSE versions < 15 are of no interest in master/octopus+.

Fixes: https://tracker.ceph.com/issues/42612
Signed-off-by: Nathan Cutler <ncutler@suse.com>