spacemanager: unknown message have to be sent to Poolmanager

as SpaceManager works as a proxy, not all messages handled as
expected.

Ticket: 7844
Acked-by: Gerd Behrmann
Target: trunk, 2.6
Require-book: no
Require-notes: yes
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>