Doing the virtme regression tests against a custom v4l-utils branch

The following is something that we might decide not to implement in media-ci, but it would be nice to have. With the current build scripts you can point to a custom version of v4l-utils. This is useful when adding a new media API/feature and you want to do the regression tests using modified v4l utilities that know about the new feature.

In media-ci this would require that you can point it to a git repo + commit containing the modified v4l-utils, and have it use that instead of the standard v4l-utils repo.

I'm not sure if it is possible, and this isn't the highest prio.