Merge pull request #1 from jaypipes/master

Adds DHCP agent recipe and fixes minor whitespace stuff
Merge pull request #2 from jaypipes/working

Add L3 Agent recipe
Create the external network bridge in L3 agent

* Adds code to establish the external network bridge
  for OpenVSwitch environment plugins (i.e. not NVP,
  BigSwitch or Plumgrid)
* Ensure ipv4 forward sysctl set on L3 Agent installs
* Adds L3 configuration option for specifying interface
  for external network bridge