luna-service2: Force LTTng tracepoints off unless explicitly enabled

:Release Notes:
LTTng tracepoints in luna-service2 are now disabled even when enabled
globally. They can re-enabled by setting (typically in a local build)
WEBOS_LTTNG_ENABLED_pn-luna-service2 = "1".

:Detailed Notes:
Enabling LTTng tracepoints in luna-service2 can cause an out of memory
condition because luna-service2 is used by many components, so they are
disabled by default.

:Testing Performed:
Checked by building.

:QA Notes:

:Issues Addressed:
[GF-45835] Put luna-service2 tracepoints behind a compile time flag

Open-webOS-DCO-1.0-Signed-off-by: Alekseyev Oleksandr <alekseyev.oleksandr@lge.com>

Change-Id: I1a7c9491cf984caa24bfad4f901b5291005570bb
Reviewed-on: https://g2g.palm.com/3914
Reviewed-by: DCO Verification
Reviewed-by: Susan Montooth <susan.montooth@lge.com>
Tested-by: Susan Montooth <susan.montooth@lge.com>