tmf: Try expanding a second time when tree expand fails

tmf: Try expanding a second time when tree expand fails

This will stabilize StandardImportAndReadSmokeTest.
Sometimes in a JFace TreeViewer, it expands to nothing.
It looks like a timing issue with an update job started by the viewer.
This is a work around until we can investigate some more.

Change-Id: I01ead54ec7ff7baaf64e1184c3a5cae8906b86a9
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/60677
Reviewed-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>