Fix return value in BaseScheduler class
Fix return value in BaseScheduler class

The return value of BaseScheduler.schedule() is expected to be iterable,
fix this for the special case that no resource_filter is defined.

Signed-off-by: Dr. Jens Harbott <4e9333fa50341cdd9f8ef6e85412fcd320f88192@osism.tech>
Change-Id: I98bf7a752506deb3343fca64c2e5d2427c4136f9

openstack/neutron,mahak/neutron,mahak/neutron,openstack/neutron,mahak/neutron,openstack/neutron