Remove & and ! pattern prefixes as early as possible

Now everything under _match_one_pattern can ignore them. This also means
that we can use the cache to return the same results for 'foo' and '!foo'.

lib/ansible/inventory/__init__.py

@@ -229,10 +229,13 @@ class Inventory(object):
     def _match_one_pattern(self, pattern):
         """ 
         Takes a single pattern (i.e., not "p1:p2") and returns a list of
-        matching hosts names. Does not take negatives or intersections
+        matching host names. Does not take negatives or intersections
         into account.
         """
 
+        if pattern.startswith("&") or pattern.startswith("!"):
+            pattern = pattern[1:]
+
         if pattern in self._pattern_cache:
             return self._pattern_cache[pattern]
 
@@ -308,9 +311,6 @@ class Inventory(object):
         hosts = []
         hostnames = set()
 
-        # ignore any negative checks here, this is handled elsewhere
-        pattern = pattern.replace("!","").replace("&", "")
-
         def __append_host_to_results(host):
             if host.name not in hostnames:
                 hostnames.add(host.name)