tmf: Fix AbstractTracePackageWizardPage tree viewer check integrity

Grayed state did not propagate correctly to parent elements.

Change-Id: Ibeaf498285622dd8a3cc7c63c92a97f7fded7593
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/37425
Tested-by: Hudson CI
Reviewed-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Tested-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>