Implement standalone network node class

Implements a standalone network node class.  A standalone network
node runs Quantum services such as a DHCP agent, L3 agent,
and/or OVS agent but does not run nova-compute (and therefore
does not house tenant/admin instances).

https://blueprints.launchpad.net/openstack-cisco/+spec/multi-dhcp-agent

Implements: blueprint bp/multi-dhcp-agent
Clean up whitespace/add missing ovs_local_ip logic
Modifications from code review

Set tunnel_ip to internal_ip by default in network node definition.

Set control class's quantum agent params to true rather than $true.
Add comments showing how to disable agents

Added comments showing how to enable/disable agents on
compute and control nodes.
Fix deprecation warnings
Merge pull request #135 from CiscoSystems/bp/multi-dhcp-agent-squash

Implement standalone network node class