Use urllib.urlencode instead of dict_to_query_str

dict_to_query_str is only used to generate 'next' links
and this part of data is not used in a cinderclient now.
So it is safe to move forward and generate correct links right now.

Change-Id: I1d7a2e0bff3827011a787b70d7c54cd6a0b5de1f
Merge "Use urllib.urlencode instead of dict_to_query_str"