rake wrapper to run puppet module tests

Some of our puppet modules have tests based using
puppetlabs_spec_helper. One would usually cd under the module and simply
invokes 'rake spec' to have a test report and repeat this for other
modules.

The default behavior checks out upstream modules to satisfy
dependencies, though, so here instead we symlink our own module dir.
This way we know whether the module will work in our environnement.

This patch adds a 'spec' task to our rakefile to easily run all modules
tests. One would invoke it like this:

 rake spec

The task does:
- lookup files named modules/*/Rakefile
- link our modules to the module fixture directory to have it run its
  tests against our env
- invoke 'rake spec_standalone' which runs the tests using the already
  existing fixtures and does not delete them on completion.

That should let us run unit tests in Jenkins with a job that simplies
does 'rake spec' and let everyone easily run all the tests by running
that command.

Change-Id: I5ea0cee53cf52f4abee243f780fa31649a7c5282
Merge "rake wrapper to run puppet module tests" into production