ceph: services: ignore health checks that ceph reports as muted

Ceph does not count a muted check towards its overall health status.
Counting it as a blocker for a rolling restart is therefore wrong, and
it also ignores what the operator wanted when muting it. This matters
now because the cephx cipher checks in Ceph 19.2.6 and 20.2.4 report a
state that an operator cannot fix while kernel clients still need the
old cipher.

OSDMAP_FLAGS stays exempt. We judge that check by the flags it lists,
so muting it to hide a permanent noscrub must not hide a nodown as
well.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>