add some Tower module integration tests (and fix a bug or two) (#37421)

* add additional test coverage for tower modules

* add test coverage for the tower_credential module

* add test coverage for the tower_user module

* fix a bug in py3 for tower_credential when ssh_key_data is specified

* add test coverage for tower_host, tower_label, and tower_project

* add test coverage for tower_inventory and tower_job_template

* add more test coverage for tower modules

- tower_job_launch
- tower_job_list
- tower_job_wait
- tower_job_cancel

* add a check mode/version assertion for tower module integration tests

* add test coverage for the tower_role module

* add test coverage for the tower_group module

* add more integration test edge cases for various tower modules

* give the job_wait module more time before failing

* randomize passwords in the tower_user and tower_group tests

lib/ansible/modules/web_infrastructure/ansible_tower/tower_host.py

@@ -100,7 +100,8 @@ def main():
     if variables:
         if variables.startswith('@'):
             filename = os.path.expanduser(variables[1:])
-            variables = module.contents_from_file(filename)
+            with open(filename, 'r') as f:
+                variables = f.read()
 
     json_output = {'host': name, 'state': state}