This is to support SLAPOS-EGG-TEST which runs tests for multiple
repositories from the same test suite. Evaluating each commit from
each repository with the result of the test result is problematic because
every time one test fail, all repositories are marked as failed.

Introduce a new property on test result repository to optionally define
the pattern of test result line to consider for this repository. This way,
with our SLAPOS-EGG-TEST running tests for slapos, slapos.core,
... etc and producing test result line with the same title as the repository
name, we can use something like `slapos$` (the pattern is a regular expression)
to match only slapos,  `slapos\.core` to match only slapos.core etc.

This also allow to define more complex relation if necessary, for example kedifa
and caucase seems related, maybe we want to configure so that a failure on kedifa
test suite marks the commits from both kedifa and caucase as failed (or maybe
not, but at least this way should make it possible)

/reviewed-on !964