Also strenghen the check to declare an unknown cap type as invalid.
Note that this means that in a mixed-version cluster, an older mon
would apply the syntax check for the older caps, even if the (say) OSDs
are newer and could parse something different. This is judged to be fine:
it is not unreasonable to ask for the mons *and* daemons to be upgraded
before using the new cap syntax or feature.
Signed-off-by: Jing Li <lijing@gohighsec.com> Signed-off-by: Sage Weil <sage@redhat.com>