The preStart snippets (graphite, carbon) try to create directories under
/var/db/. That currently fails because the code is run as user
"graphite". Fix by setting "PermissionsStartOnly = true" so that the
preStart stuff is run as 'root'.
Further:
* graphite-web-0.9.12/bin/build-index.sh needs perl, so add it to PATH.
* Now that preStart runs as root, we must wait with "chown graphite"
until we're done creating files/directories.
* Drop needless check for root (uid 0) before running chown.
ffb593f880