tasks: typo in mds_client_recovery

Signed-off-by: John Spray <john.spray@redhat.com>
tasks: rename FuseMount.get_client_id to get_global_id

'client_id' was ambiguous because in other places it
meant the '0' in client.0, whereas here it means
the runtime-generated global ID of the client.

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