mon: forbid 'mds rmfs' while daemons are running

This avoids the need to do anything clever about kicking
out MDS daemons during a rmfs: we push that responsibility
onto the admin to run 'mds stop' or somestuch first.

Signed-off-by: John Spray <john.spray@inktank.com>
mon/MDSMonitor: add fs_name

newfs and rmfs commands now refer to the
filesystem by name, so that in future these
commands can support a multi-filesystem
model.

rmfs when no filesystem exists is now a
warning rather than an error.

Signed-off-by: John Spray <john.spray@inktank.com>
vstart: update for newfs/rmfs changes

Signed-off-by: John Spray <john.spray@inktank.com>
qa: update for newfs/rmfs changes

Signed-off-by: John Spray <john.spray@inktank.com>
test/cli: Update for only 1 default pool

Tests for osdmaptool previously assumed that --createsimple
would always result in at least 3 pools.

Signed-off-by: John Spray <john.spray@inktank.com>
mon: hide mdsmap in 'ceph status' if not enabled

Previously we checked if the MDS map had ever been
updated (epoch > 1), now we have an explicit flag
for whether it's enabled.

Signed-off-by: John Spray <john.spray@inktank.com>