Because "." is a field separator for graphite, we're incorrectly
nesting the results.
A better idea seems to be to store these stats under the job name.
That's going to be more helpful when looking up in Zuul build results
anyway.
Follow-on to I90dfb7a25cb5ab08403c89ef59ea21972cf2aae2
Change-Id: Icbb57fd23d8b90f52bc7a0ea5fa80f389ab3892e