Update .travis.yml

Install Puppet on the test VM
Update .travis.yml
Trying to understand why Puppet tests do not work on Travis
Another try to use Puppet on Travis
Last try for tonight
Another try
Yet another try...
Try to install both gems
Display why Puppet does not run on Travis
Trying something
Update .travis.yml
Update .travis.yml
Merge remote-tracking branch 'origin/master'

Conflicts:
	roboconf-plugin-puppet/src/test/java/net/roboconf/plugin/puppet/PluginPuppetTest.java