linaro-watchdog repository needs a branch to be specified

[Milo Casagrande]

With the migration to the new staging instance of patchmetrics, we discovered a repository that, when cloned, does not have a default branch sets, resulting in an error from the git operation.

Since patchmetrics does not support branch specification in its DB, we hard-code some of these values directly in its code.
We are already doing so for a couple of projects.

In this case, we need it for linaro-watchdog.
The new instance of patchmetric should be live early next week.