add validate_territory validator

api/validators.py

@@ -1,4 +1,5 @@
 # coding=UTF-8
+from api.models.market import iter_markets
 from api.exceptions import ValidationError
 
 
@@ -7,3 +8,10 @@ def validate_keys_exists(obj, *keys):
         if not key in obj:
             raise ValidationError('No {} is specified'.format(key))
     return True
+
+
+def validate_territory(value):
+    for market in iter_markets():
+        if market.territory == value:
+            return True
+    raise ValidationError('{} is not a valid territory'.format(value))