Update to the latest stevedore

Use a version of stevedore that does not try to
install distribute.

The requirements change is in
https://review.openstack.org/#/c/32738/

Change-Id: I74bc6013710965401b7e64abc8827a46c817fd56
Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>
Merge "Update to the latest stevedore"