changes ovs agent_id init to use hostname instead of mac

changes ovs agent_id init to use hostname instead of mac

In the Open vSwitch agent,
the Agent id is currently based off the mac address of the br-int.
Userspace only Open vSwitch derivatives such as Intel's DPDK
Accelerated Open vSwitch do not currently create a tap device in the kernel
to back the ovs bridges local port.
This limitation prevents reuse of the OpenVSwitch agent between both switches.

To enable reuse of the ovs agent with Intel's DPDK Accelerated Open vSwitch,
the proposal is to change the  generation of the  agent_id to use the hostname,
instead of the mac address of the br-int.

For several plugins such as the nec,mlnx,hyperv and onconvergence agents
the hostname is used to create the agent id.
Using the hostname will normalise the agent_id between these 5 neutron agents,
additionally log readability will also be improved,
if log aggregation is preformed across a cluster
as it will be easier to identify which node the log is from.

the hostname is retrived from cfg.CONF.host

Closes-Bug: #1323259
Change-Id: I9abfac17a74d298f1a17a0931fc98ac00234ac0b