Improve OVS agent logging for profiling

This patch adds some debug logging statements aimed at profiling
tasks in the agent's main rpc loop.
These logging capabilities will help gain some better insights into
the performance bottlenecks of the agent.

Part of blueprint neutron-tempest-parallel

Change-Id: Ied04b906dbbb9993283981bdee6c96e43a7d19a3
Merge "Improve OVS agent logging for profiling"