Adding license checks for Tower inventory source

* For Tower the license must match between the source and destination
* For AWX the check is disabled
* Hosts imported from another Tower don't count against your license
  in the local Tower
* Fix up some issues with enablement
* Prevent slashes from being used in the instance filter
* Add &all=1 filter to make sure we pick up all hosts

awx/main/tasks.py

@@ -1914,6 +1914,7 @@ class RunInventoryUpdate(BaseTask):
                     env[str(env_k)] = unicode(inventory_update.source_vars_dict[env_k])
         elif inventory_update.source == 'tower':
             env['TOWER_INVENTORY'] = inventory_update.instance_filters
+            env['TOWER_LICENSE_TYPE'] = get_licenser().validate()['license_type']
         elif inventory_update.source == 'file':
             raise NotImplementedError('Cannot update file sources through the task system.')
         # add private_data_files