ceph: quota: add counter for snaprealms with quota

ceph: quota: add counter for snaprealms with quota

BugLink: https://bugs.launchpad.net/bugs/1834235
By keeping a counter with the number of snaprealms that have quota set
allows to optimize the functions that need to walk throught the realms
hierarchy looking for quotas.  Thus, if this counter is zero it's safe to
assume that there are no realms with quota.

Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
(cherry picked from commit d557c48db730eaab6b75d4af332c135309b7a6a4)
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>