Fix puppetlabs-concat usage to become compliant with v1.0.4.

* puppetlabs-concat v1.0.4 is the latest version supported by puppetlabs.
* This module was using `ensure` parameter on the `concat` type even if this parameter is not yet available in v1.0.4 and puppet-remctl Modulefile pretends that puppetlabs-concat v1.x is compatible.
* With no possibility to `ensure` that the final concatenated file is _absent_, when no command is defined, an empty file with only _WARNINGS_ is left on the host (i.e there is no way to actually really remove an empty command file)
Prepare for v2.1.1

* Update CHANGELOG
* Update Modulefile
Multiple fixups

* Fixup some puppet-lint stuff:
 - Specify that puppet-lint should be run according to local directory (add '--relative' option to puppet-lint).

* Ignore Gemfile.lock
Merge branch 'hotfix/v2.1.1'