Fix fact gathering module being absent

Somewhere recently we broke the ability to gather multiple modules in
one scan job pass.   This fixes that, it also further improves the scan
job performance.

awx/plugins/fact_caching/tower.py

@@ -50,7 +50,7 @@ class CacheModule(BaseCacheModule):
     def __init__(self, *args, **kwargs):
         # Basic in-memory caching for typical runs
         self._cache = {}
-        self._cache_prev = {}
+        self._all_keys = {}
 
         # This is the local tower zmq connection
         self._tower_connection = C.CACHE_PLUGIN_CONNECTION
@@ -72,12 +72,10 @@ class CacheModule(BaseCacheModule):
     def identify_new_module(self, key, value):
         # Return the first key found that doesn't exist in the
         # previous set of facts
-        if key in self._cache_prev:
-            value_old = self._cache_prev[key]
-            for k,v in value.iteritems():
-                if k not in value_old:
-                    if not k.startswith('ansible_'):
-                        return k
+        if key in self._all_keys:
+            for k in value.iterkeys():
+                if k not in self._all_keys[key] and not k.startswith('ansible_'):
+                    return k
         # First time we have seen facts from this host
         # it's either ansible facts or a module facts (including module_setup)
         elif len(value) == 1:
@@ -110,7 +108,7 @@ class CacheModule(BaseCacheModule):
         # Assume ansible fact triggered the set if no new module found
         facts = self.filter_ansible_facts(value) if not module else dict({ module : value[module]})
         self._cache[key] = value
-        self._cache_prev = copy(self._cache)
+        self._all_keys[key] = value.keys()
         packet = {
             'host': key,
             'inventory_id': os.environ['INVENTORY_ID'],