Move the script here from
http://jenkins.osmocom.org/jenkins/job/Osmocom_nightly_packages/
The jenkins job shall call this script instead.
One change: instead of 'rm -rf *', rather check for an empty dir, to not
endanger valuable data a user may have around when invoking this script out of
curiosity.
I've been asked at least twice what the contents of the expected env
vars should be, so log an example on error.
Change-Id: I635752e6033c57bfce90d8b0732bc402bf3014c8