Nova uses RabbitMQ on Ubuntu/Debian/openSUSE

Added steps to configure Nova to use the RabbitMQ
messaging system on Ubuntu, Debian, and openSUSE.

Change-Id: I3a3e6cecb45a292a55d7a83f2473bec2ec279027
Merge "Nova uses RabbitMQ on Ubuntu/Debian/openSUSE"