set-root-authorized-keys does not fail when there is no metadata
available, causing the error resulting from it to appear in
/root/.ssh/authorized_keys, so running script with -e to let it fail
fast. would also be nicer if mdata-get would print the error to
stderr in stead of stdout.

Also add a fix by Jasun from JoyentCloud, adding newlines for each ssh-rsa, ssh-dss.