Reports artifact links added

[Martin Packman]

I have deployed code on juju-reports that directly links all build
artifacts from the test detail page.

For instance see one of the recent runs:

<http://reports.vapour.ws/releases/2312>

In the "Last build" column darker shading indicates you can hover the
cell to reveal more links, which can include:

* Previous builds and their logs - a number of jobs may be run
multiple times in order to get a pass, the earlier failures are now
easy to access.
* Juju logs from failed tests such as the machine and unit logs.
* The binaries used in the tests for all platforms, in the build-* jobs.

The direct link to the jenkins job pages is also back, note these will
expire unlike the artifact links, so may lead nowhere for historic
runs.

I plan to make the gziped logs directly openable in the browser and
tweak the css display a little more. I'm like to hear any more
suggestions or feedback on what would be useful to see here.

Martin