Update passenger recipe to accept custom ruby install with rvm cookbook

Hello,

I am using this [rvm cookbook](https://github.com/fnichol/chef-rvm) for my provisioning, so I added the possibility to change the ruby used when installing passenger.

I might have forgotten things to change, but this was enough for my usage (chef-solo), please let me know if this is something you'd like to integrate here.

Cheers,
Paul