Changes

jenkins: properly clean previous artifacts
Drop the second 'rm -f' from the rm shell command (typo).
Remove all artifacts matching *.build-*.{tgz,md5} because if a job
changes the name of its artifact, the previous artifacts would remain.
(I hit this with the new scripts being originally wrong and all
producing
'osmo-msc.*' artifacts, and those stuck around in the workspace even
after the name was fixed.)
Change-Id: I00d246226f4c723696bb737ed707cfd0e4c33714