Cleanup log marker in neutronv2 api

Cleanup log according to docs.openstack.org/developer/oslo.i18n/guidelines.html
Add LI marker for LOG.info.
Correct debug log information in _get_instance_nw_info function.
and other log cleanup.

Change-Id: Ic7fba3e750196dfb3296291cd4d4d21bc06d47c6
Merge "Cleanup log marker in neutronv2 api"