mgr: store declared_types in MgrSession

mgr: store declared_types in MgrSession

Because we don't (yet) properly prevent multiple sessions
from daemons reporting the same name (e.g. rgws), storing
it in the DaemonPerfCounters meant that one daemon's report
was referring to another daemon's set of reported types.

This should always have been a property of the session.

The behaviour will still be ugly when multiple daemons
are using the same name (stomping on each other's stats/statsu)
but it shouldn't crash.

Fixes: http://tracker.ceph.com/issues/21197
Signed-off-by: John Spray <john.spray@redhat.com>
(cherry picked from commit dc415f1ae09a308bd448614934a4c168eb9cf07b)