Tycho 1.2.0 is only able to start tests with org.eclipse.equinox.ds
nstalled (configuring its start level).
However, org.eclipse.equinox.ds is now discarded and
org.apache.felix.scr replaces it as provider for `osgi.extender`. Tycho
1.2.0 is not able to set the right start level for
org.apache.felix.scr.
So we explicitly add org.eclipse.equinox.ds to keep compatility with
Tycho 1.2.0: Tycho sets a start-level for org.eclipse.equinox.ds, so
when the bundle starts it also starts org.apache.felix.scr (as
requirement).

Change-Id: Id03001f415586e3ab0bcb7844fdef84555cc133d
Signed-off-by: Mickael Istria <mistria@redhat.com>