Tweaks to pip-download

Have the output of pip-download be more
intituive and informative, also clear the
download dir target before running by
default to avoid unwanted dependencies from
getting included. Add a nice little spinner
that is shown when downloading.

Change-Id: I23acd5021fe95e7ce48f60182daa332b76191ccc
Add in building of oslo.messaging

Closes-Bug: 1260892

Change-Id: Id5d52bbcba10211349b30e69cbd4b91e3106c9bb
Merge "Tweaks to pip-download"