Currently, the dhcp Provisioning of ports is the crucial bottleneck
of that concurrently boot multiple VM.
The root cause is that these ports will be processed one by one by dhcp
agent when they belong to the same network, And the 'Provisioning complete'
port is still blocked other port's processing in other dhcp agents. The
patch aim to optimize the dispatch strategy of the port cast to agent to
improve the Provisioning process.
In server side, I classify messages to multi levels. Especially, I classify
the port_update_end or port_create_end message to two levels, the high-level
message only cast to one agent, the low-level message cast to all agent. In
agent side I put these messages to `resource_processing_queue`, with the queue,
We can delete `_net_lock` and process these messages in order of priority.
Additonally, I modified the `resource_processing_queue` for my demand. I update
`_queue` from LIST to PriorityQueue in `ExclusiveResourceProcessor`, by this
way, we can sort all message which cached in `ExclusiveResourceProcessor` by
priority.
Related-Bug: #1760047
Change-Id: I255caa0571c42fb012fe882259ef181070beccef
99f4495c94