rake mock[<provider>] and live[<provider] tasks

In a case of inspired laziness, I decided I'd rather implement this:

```sh
$ rake -vT
...
rake live[provider]  # Run live tests against a specific provider
rake mock[provider]  # Run mocked tests for a specific provider
...
```

```sh
$ rake mock['rackspace']
# runs rackspace tests using mocks...
```

then send someone instructions to run `export FOG_MOCK=false && bundle exec shindont tests/rackspace` or `export FOG_MOCK=false && bundle exec shindont tests/rackspace`.  Less typing.

Note: the provider names are from the tests folder instead of the keys for Fog.providers.  It's the same for most, but there is are discrepencies for multi-word providers (gogrid, internetarchive, baremetalcloud, stormondemand, vclouddirector and vmfusion).