Improve Tower integration test support:

- Add TOWER_VERSION environment variable.
- Add error check for missing configuration.

test/runner/lib/cloud/tower.py

@@ -205,6 +205,7 @@ class TowerConfig(object):
         :rtype: dict[str, str]
         """
         env = dict(
+            TOWER_VERSION=self.version,
             TOWER_HOST=self.host,
             TOWER_USERNAME=self.username,
             TOWER_PASSWORD=self.password,
@@ -231,6 +232,11 @@ class TowerConfig(object):
         values = dict((k, parser.get('general', k)) for k in keys)
         config = TowerConfig(values)
 
+        missing = [k for k in keys if not values.get(k)]
+
+        if missing:
+            raise ApplicationError('Missing or empty Tower configuration value(s): %s' % ', '.join(missing))
+
         return config