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/managers.py

@@ -7,7 +7,7 @@ import logging
 
 from django.db import models
 from django.utils.timezone import now
-from django.db.models import Sum
+from django.db.models import Sum, Q
 from django.conf import settings
 
 from awx.main.utils.filters import SmartFilter
@@ -21,9 +21,9 @@ class HostManager(models.Manager):
     """Custom manager class for Hosts model."""
 
     def active_count(self):
-        """Return count of active, unique hosts for licensing."""
+        """Return count of active, unique hosts for licensing. Exclude ones source from another Tower"""
         try:
-            return self.order_by('name').distinct('name').count()
+            return self.filter(~Q(inventory_sources__source='tower')).order_by('name').distinct('name').count()
         except NotImplementedError: # For unit tests only, SQLite doesn't support distinct('name')
             return len(set(self.values_list('name', flat=True)))