Added ability to add pytest tests

Until now ansible-freeipa repository only had playbook tests. This
commit introduces the ability of creating TestCase classes connected to
the master host. This connection can be used to run commands in the
managed host after the ansible playbook execution is the allowing the
verification of the machine state.

requirements-tests.txt

@@ -0,0 +1,6 @@
+-r requirements.txt
+pytest>=2.7
+pytest-sourceorder>=0.5
+pytest-split-tests>=1.0.3
+testinfra>=5.0
+jmespath>=0.9  # needed for the `json_query` filter