Accessing the log of an autopkgtest should be one-click

In Britney, clicking on "Regression or new test" (or "Pass",...) gives one-click access to the log of an autopkgtest.

Debusine requires 3 clicks (autopkgtest <arch> → Output <number> → log), which is too much for packages triggering a non-trivial number of reverse dependencies where even after #659 (closed) is fixed having to manually check a two digit number of autopkgtest regressions is expected.