Code cleanup: use oslo's to_slug() instead of slugify()

The bash completion code is the sole user of the slugify() function
in utils, which is substantially similar to to_slug() provided in
strutils from oslo.

Change-Id: Ib4eb7e4c0fa0e9bc5c4a0856f6391911d8f8fd3b
Closes-bug: #1266118
Remove class_name parameter from quota_class

class_name parameter is not used in both Nova v1.1/v3 API.
Nova considers the part of url as class_name.
For example, bar is considered as class_name in the following case:
 curl -i 'http://localhost:8774/v3/os-quota-class-sets/bar' -X PUT ..

This patch removes this unused paramter from quota_class.

Change-Id: Id4eba5b2a17506bc04ea23ef1097ef9cdb9caf8a
Merge "Code cleanup: use oslo's to_slug() instead of slugify()"