Adding puppet-rspec tests

Reasons:
- No rspec tests

Changes:
- Add dependencies in Gemfile.
- Edit Rakefile to add the capability to use "bundle exec rake test" command
to check lint and spec.
- Add some tests for class, type and provider.

Change-Id: I62653b883340a43a0cddd1fea36773d6c56a48f9
System need libffi-dev

The system need libffi-devel to allow pip to install all dependencies on
RedHat systems.

Additionally, a requirement is required for development packages to be
installed before creating the virtual env.

Change-Id: I8597b4438f0ce9830a63337a4a8073765eb9615a
Closes-Bug: 1286167
Merge "Adding puppet-rspec tests"