tmf: Bug 491548: Do not incrementally build full time graph event list

The full event list should be recomputed for the full range at every
iteration of the build thread. If built incrementally it can create too
many events in the full event list.

The build thread should not insert NullTimeEvent in the full event list.

Change-Id: I2523291197b2d93267b2aa799e6126ea74eea0f9
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/70519
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>