Force plugins to execute using LANGUAGE='C'.

IPA translates exception messages and Ansible uses controller's
language to execute plugins on target hosts, and since ansible-freeipa
uses Exceptions messages to detect some errors and/or states, using any
language that has a translation for the required messages may cause the
plugin to misbehave.

This patch modifies ansible_freeipa_module in plugin/module_utils to
force the use of "C" as the language by setting the environment variable
LANGUAGE.

Tests were added to verify the correct behavior:

    tests/environment/test_locale.yml

The first test will fail, if ansible_freeipa_module is not patched, with
the message:

   host_show failed: nonexistent: host nicht gefunden

This issue is not present if the language selected does not provide
a translation for the eror message.

This patch does not fix encoding issues that might occur in certain
releases (e.g.: CentOS 8.3).

Fix #516