Add acceptance tests for platforms without Bash
Ensure all remote commands are executed with `sh`.

This ensures the plugin executes all remote commands with `sh` as some
*nixes don't ship with Bash!

Fixes #69.
Update development/test dependancies to Vagrant 1.5
Add a `.ruby-version` file. Default to 2.0.0-p353.

This matches the version Vagrant ships in it's packages.