Fix Jenkins build the wrong revision.
Fix Jenkins build the wrong revision.

The problem is that AUTOREV which is used in the Mender recipe is not
checked for an updated revision if nothing else has changed in the
meta-mender repository, which is something we need. So instead, we let
Jenkins clone an updated version.

The fix is threefold:

- The fix in this commit, which enables building from an external
  source (where Jenkins has pre-cloned the repo).
- Adding the cloning of the mender repository to Jenkins.
- Making sure that the location of the mender repository is appended
  to the local.conf file in the Jenkins recipe, since we cannot refer
  to the Jenkins environment variables directly from bitbake.

mendersoftware/meta-mender-qemu