Add appscale install script for OSX

Already created wiki page at https://github.com/AppScale/appscale-tools/wiki/Installing-the-appscale-tools-on-mac-os-x

The install script uses the [homebrew](http://mxcl.github.com/homebrew/) package manager for OSX. Macports is not supported.

euca2ools-2.1.0 is installed from source.