Update urls for images
Workaround pyghmi requirement bug

pyghmi install of 0.5.9.1 is broken. Mask that version.

Basically patches us for:
https://review.openstack.org/#/c/74246/
openstack-bug: https://bugs.launchpad.net/openstack-ci/+bug/1281385
Remove busybox image

Devstack no longer uses the busybox image, so
we no longer need to download or load it.

Note that this merge may need to be reverted
should someone attempt to create a Havana branch.
Merge branch 'up' into openstack-ci