core: Added DAO for HostNetworkQos entities

Added DAO for these new entities, and a corresponding test class.

Placement of the "network" and "qos" tables in fixtures.xml had to be
swapped, as network entries might depend on the existence of of qos
entries.

Change-Id: I90535167d324c80aa9de7a735a010818ab45e428
Signed-off-by: Lior Vernia <lvernia@redhat.com>