add Rackspace provider acceptance test
add provider parameter to test:acceptance Rake task

This will allow the running of acceptance tests for a single provider.
By default tests will be run against ALL THE PROVIDERS (previous
behavior).
ensure 'vagrant-rackspace/action' is loaded; fixes GH-7

The `VagrantPlugins::Rackspace` module is missing the autoload for
`VagrantPlugins::Rackspace::Action` so we need to ensure it is
loaded before accessing the module in an after hook.
trigger plugin if machine state is :active; fixes GH-8

The `rackspace` provider set's the machine state to `:active`
instead of `:running` like other providers.

We'll also rename the `IsRunning` action to `IsRunnningOrActive` to
reflect the updated logic.
update to latest vagrant-aws (0.2.1)

This allows the chef-solo provisioner to work correctly again:
https://github.com/mitchellh/vagrant-aws/issues/49