control: Bug 483560: Refresh UI once after adding all children events

control: Bug 483560: Refresh UI once after adding all children events

This will redraw the tree only once after all children event components
are added for channels, ust and kernel provider. Before this change the
UI was redrawn after each event.

Change-Id: If48ac0740be8884bcf52bb7f3da4a15859a3639f
Signed-off-by: Bernd Hufmann <Bernd.Hufmann@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/62200
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>