Fix the remove property logic in V2

The check used to verify if there are any properties to remove in the V2
image-update command will always execute even if there are no properties to
remove due to the fact that it checks if remove_prop is not None, when it is
actually a list and not a None value.

Closes-Bug: #1475053
Change-Id: Ia36e945b880de3514c73073a392bdb7dde13cf84

glanceclient/v2/images.py

@@ -250,7 +250,7 @@ class Controller(object):
             except warlock.InvalidOperation as e:
                 raise TypeError(utils.exception_to_str(e))
 
-        if remove_props is not None:
+        if remove_props:
             cur_props = image.keys()
             new_props = kwargs.keys()
             #NOTE(esheffield): Only remove props that currently exist on the