ctf: Restore the downloading of the ctf-testsuite

ctf: Restore the downloading of the ctf-testsuite

When we migrated to using the tracecompass-test-traces, we also stopped
downloading the ctf-testsuite using git. However those are not part of
tracecompass-test-traces. Oops!

Somehow the tests didn't complain so far, but it'd be better if they
actually ran.

Change-Id: Id6b81698bf8e85d840819db8505a95f57a51685c
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/59438
Reviewed-by: Hudson CI
Reviewed-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Tested-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>