Catch appropriate KeyError instead of any exception

resourceManager.registerNamespace() raises a KeyError exception.
Calling methods were catching any exception, treating all as
KeyError, which means non-KeyError exceptions were swallowed. Now only
KeyErrors are caught and logged as info (instead of warn), and other
potential exceptions are not caught at all, i.e., not swallowed
anymore.

Change-Id: Ifc0fa5ca50e4eb78d62fd3cdc8b09723486bcaa0
Signed-off-by: Vered Volansky <vvolansk@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/13617
Reviewed-by: Dan Kenigsberg <danken@redhat.com>