Use Python2/3 to detect ansible_python_interpreter

With the test it is not needed to pin down the python interpreter for ansible
modules. It is therefore possible to use a Python2 version on Fedora-27 and
a Python3 version on Fedora-26.

roles/ipaclient/tasks/python_2_3_test.yml

@@ -0,0 +1,15 @@
+- block:
+  - name: Verify Python3 import
+    command: python3 -c "from ipapython.version import NUM_VERSION"
+    register: py3test
+    failed_when: False
+
+  - name: Set python interpreter to 3
+    set_fact:
+      ansible_python_interpreter: "/usr/bin/python3"
+    when: py3test.rc == 0
+
+  - name: Set python interpreter to 2
+    set_fact:
+      ansible_python_interpreter: "/usr/bin/python2"
+    when: py3test.failed or py3test.rc != 0