Add more log when dhcp agent sync_state.
Add more log when dhcp agent sync_state.

DHCP agent output no log when synchronizing network state, it's hard to observe
agent work state through log.

Add log to indication status and progress of sync state process:
 * Agent has fetched all active networks
 * Agent configure a network start and finish

Closes-Bug: #1535285

Change-Id: I517073e4a9a7a870cbbfd8cb0e14a7571176f562

huntxu/neutron,noironetworks/neutron,mahak/neutron,eayunstack/neutron,klmitch/neutron,cloudbase/neutron,openstack/neutron,sebrandon1/neutron,mahak/neutron,cloudbase/neutron,eayunstack/neutron,MaximNevrov/neutron,wolverineav/neutron,klmitch/neutron,bigswitch/neutron,MaximNevrov/neutron,openstack/neutron,igor-toga/local-snat,bigswitch/neutron,sebrandon1/neutron,huntxu/neutron,dims/neutron,noironetworks/neutron,mahak/neutron,igor-toga/local-snat,dims/neutron,wolverineav/neutron,openstack/neutron