test: add test_unit.yml to run unit tests

This requires to make "library/network_connections.py" more
independent from ansible modules

In the end, the Python code runs on the target machines,
with the python installed there. So, it makes sense to also
run the unit tests as part of the CI tests.

test/test_unit.yml

@@ -0,0 +1,34 @@
+---
+- hosts: all
+  name: execute python unit tests
+  tasks:
+    - copy:
+        src: /role/library/network_connections.py
+        dest: /tmp/test-unit-1/
+
+    - copy:
+        src: /role/library/test_network_connections.py
+        dest: /tmp/test-unit-1/
+
+
+    - package:
+        name: python2
+        state: present
+      ignore_errors: true
+      register: python2_available
+
+    - command: python2 /tmp/test-unit-1/test_network_connections.py
+      when: python2_available | succeeded
+
+
+    - package:
+        name: python3
+        state: present
+      ignore_errors: true
+      register: python3_available
+
+    - command: python3 /tmp/test-unit-1/test_network_connections.py
+      when: python3_available | succeeded
+
+
+    - command: python /tmp/test-unit-1/test_network_connections.py