remove build_tempest

we haven't actually used this script in about a year, in favor of
the actual in tree lib/tempest.

Change-Id: I9d78b395846ebe833a38ba50edae226040cd7f45
Merge "remove build_tempest"
Merge commit 'refs/changes/99/70999/4' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch