jenkins-setup-build-environment: delete libvirt images before test run

profitbricks-build7-amd64 was running out of disk space when running this
job...

jenkins-setup-build-environment

@@ -50,6 +50,12 @@ fi
 export VAGRANT_HOME=$WORKSPACE/vagrant.d
 mkdir $VAGRANT_HOME
 
+# delete leftovers from previous run
+virsh -c qemu:///system undefine buildserver_default \
+      --nvram --managed-save --remove-all-storage --snapshots-metadata || true
+virsh -c qemu:///system undefine builder_default \
+      --nvram --managed-save --remove-all-storage --snapshots-metadata || true
+
 cd $WORKSPACE
 echo "debian_mirror = 'https://deb.debian.org/debian/'" > $WORKSPACE/makebuildserver.config.py
 echo "boot_timeout = 1200" >> $WORKSPACE/makebuildserver.config.py