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
diff --git a/contrib/jenkins-build-common.sh b/contrib/jenkins-build-common.sh
index e15c616..a5b34af 100644
--- a/contrib/jenkins-build-common.sh
+++ b/contrib/jenkins-build-common.sh
@@ -56,7 +56,7 @@
 env | grep -v "^LESS" | sort
 
 # clean the workspace
-rm -f "$base/${name}"*.tgz rm -f "$base/${name}"*.md5
+rm -f "$base"/*.build-*.{tgz,md5}
 rm -rf "$prefix_real"
 mkdir -p "$prefix_real"