Avoid use xx=[] for parameter in function

Use xx = [] for the parameter for function, this parameter will
only be initialized at the first call, this is should be avoided.
Better choice is to set the initial value to None, then the initialization
time use xx= xx or []

more information:http://effbot.org/zone/default-values.htm

Change-Id: Icbade7dd4c7d231ae65fd4f8de673b484bab721c

troveclient/common.py

@@ -42,7 +42,9 @@ def quote_user_host(user, host):
 
 class Paginated(list):
 
-    def __init__(self, items=[], next_marker=None, links=[]):
+    def __init__(self, items=None, next_marker=None, links=None):
+        items = items or []
+        links = links or []
         super(Paginated, self).__init__(items)
         self.next = next_marker
         self.links = links

troveclient/compat/common.py

@@ -399,10 +399,10 @@ class Paginated(object):
        next property you can use to get the next page of data.
     """
 
-    def __init__(self, items=[], next_marker=None, links=[]):
-        self.items = items
+    def __init__(self, items=None, next_marker=None, links=None):
+        self.items = items or []
         self.next = next_marker
-        self.links = links
+        self.links = links or []
 
     def __len__(self):
         return len(self.items)

troveclient/v1/management.py

@@ -272,7 +272,8 @@ class MgmtDatastoreVersions(base.ManagerWithFind):
                          "version")
 
     def create(self, name, datastore_name, datastore_manager, image,
-               packages=[], active='true', default='false'):
+               packages=None, active='true', default='false'):
+        packages = packages or []
         """Create a new datastore version."""
         body = {"version": {
             "name": name,
@@ -287,7 +288,8 @@ class MgmtDatastoreVersions(base.ManagerWithFind):
         return self._create("/mgmt/datastore-versions", body, None, True)
 
     def edit(self, datastore_version_id, datastore_manager=None, image=None,
-             packages=[], active=None, default=None):
+             packages=None, active=None, default=None):
+        packages = packages or []
         """Update a datastore-version."""
         body = {}
         if datastore_manager is not None: