Add support for master/slave mysql

This patch adds two new parameters for
the haproxy/mysql class that enables setting
a master for mysql clusters that will handle
all load, with the other nodes serving as
backups
Fix undef error in base firewall

before cannot be set to undef.
Remove errant +
Add DNS support to test_nova

This adds public DNS to the subnet for the public
subnet in the test, and changes the test to try
pinging www.google.com.

This will only pass if the node where it runs has
been configured to route traffic from the public
network correctly.