Fix for LAMP on vSphere and Openstack.

- Add an rs-mysql/bind_address attribute that defaults to nil, but if set
  will be used instead of looking up the public or private address to use
  for mysql/bind_address.
Document rs-mysql/bind_address behavior [ci skip]
Merge pull request #16 from rightscale-cookbooks/white_14_06_acu169654_lamp_bind_address

Fix for LAMP on vSphere and Openstack.