Lower ML2 message severity.
Lower ML2 message severity.

Logging that a network has no segments as an error
message when it doesn't impact execution pollutes
logs.  Lower the message severity to debug.

Change-Id: I7d88581b4703e7c287cec9406dd093089db8595c
Closes-Bug: #1597362
Signed-off-by: Ryan Moats <7ac70bcc48c94124ee1b01a4779bf5a8a6faebbd@us.ibm.com>

huntxu/neutron,mahak/neutron,noironetworks/neutron,noironetworks/neutron,igor-toga/local-snat,igor-toga/local-snat,cloudbase/neutron,openstack/neutron,eayunstack/neutron,mahak/neutron,cloudbase/neutron,openstack/neutron,openstack/neutron,mahak/neutron,sebrandon1/neutron,sebrandon1/neutron,huntxu/neutron,eayunstack/neutron