mon: fix tell to hybrid octopus/pre-octopus mons

mon: fix tell to hybrid octopus/pre-octopus mons

We can't decide whether to use the new tell command style based on the
monmap.min_mon_release alone because some mons may be octopus even though
that hasn't updated yet.  The same goes for if we look at the combined
features for the cluster--the underlying problem is the monmap doesn't
tell us which mons are octopus and which ones aren't, so we don't know
how to behave.

Instead, allow octopus+ mons to advertise the converted tell commands
going forward, for compatibility with pre-octopus clients (who do the old
style of tell) and for octopus+ clients talking to a min_mon_release <
octopus cluster.

Signed-off-by: Sage Weil <sage@redhat.com>