mon: prevent cache pools being used CephFS

Fixes two things:
 * EC pools are now permissible if they have a cache overlay
 * Pools are not permissible if they are a cache tier.

Fixes: #9435

Signed-off-by: John Spray <john.spray@redhat.com>
mon: forbid tier changes when in use by FS

* Removing tiers from a base pool in use by CephFS is forbidden.
* Using CephFS pools as tiers is forbidden.

Signed-off-by: John Spray <john.spray@redhat.com>
Merge pull request #2507 from ceph/wip-9435

#9435 - enforce rules for using EC/tiered pools with CephFS

Reviewed-by: Greg Farnum <greg@inktank.com>