(#11860) Add a (pending) acceptance test to check LANG during user "exec"s

Add an acceptance test that validates that when a manifest contains an "exec", it will be executed using the default system / user locale rather than forcing the locale to 'C'.

Note that this test is in "pending" for two reasons:

1. It requires the spanish locale package(s) to be installed on the agent node(s). (e.g., apt-get install language-pack-es-base ).
2. It depends on some new functionality in the puppet-acceptance framework, so the test shouldn't be made active until after the following pull request has been merged:

https://github.com/puppetlabs/puppet-acceptance/pull/123