Adds the __main__ conditional check (#2098)

As is done in other ansible modules, this adds the __main__ check
to the module so that the module code itself can be used as a library.
For instance, when testing the code.

lib/ansible/modules/extras/network/f5/bigip_node.py

@@ -379,5 +379,6 @@ def main():
 # import module snippets
 from ansible.module_utils.basic import *
 from ansible.module_utils.f5 import *
-main()
 
+if __name__ == '__main__':
+    main()