sp: receive domains map in connectStoragePool

This patch adds the support for the StoragePoolMemoryBackend and
the required support in the HSM class to instantiate it and to
live upgrade from older backends.

The connectStroagePool API has been updated to receive the extra
domainsMap dictionary that triggers the use of the new backend.

Change-Id: I393677f643a62e3711af2a3cfb8b4b9a5ce11c2d
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/21427
Reviewed-by: Ayal Baron <abaron@redhat.com>