Added Ubuntu support. Now using couchbase pkg defaults

The following changes have been made and tested with SL-6.2 and Ubuntu-12.04.2:

* Added Ubuntu & system arch package support (in attributes/default.rb)
* Updated instance provider to use coucbase's default moxi-cluster.cfg file in order to maintain compatibility with the rpm/deb package's supplied init script.
* Updated default.rb recipe: it now installs moxi package, configures a default moxi-cluster.cfg instance, and starts moxi-server