crimson/mgr: reconnect in ms_handle_reset()

crimson/mgr: reconnect in ms_handle_reset()

since `reconnect()` does not wait for `conn->close()` anymore, we
can actually call `reconnect()` right in `ms_handle_reset()`.

also, to avoid connecting mgr too frequently, connect the mgr with
specified interval (1 second by default).

send the MMgrOpen message in `ms_handle_connect()` to make it explicit
that we sends this message when the connection is established.

Signed-off-by: Kefu Chai <kchai@redhat.com>