mgr: always bootstrap mgr right after the mon

mgr: always bootstrap mgr right after the mon

If we don't bootstrap the mgr after the mon and the osds handler are
called, we will never be able to reach a clean state since the pgs
stats are handled by the mgr. This also happens when doing daemon
collocation.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1493920
Signed-off-by: Sébastien Han <seb@redhat.com>