testing/download: GIT use BRConfigTest

Enables the test to use the new non-emulator base class which takes
significantly less test time.

Cc: Ricardo Martincoski <ricardo.martincoski@datacom.ind.br>
Signed-off-by: Matthew Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>