Don't log TRACE info in notify_about_instance_usage

Exception information was added to notifications a while back and
logging of tracebacks from those exceptions was added as well.  This can
be confusing because the exception information may be suppressed where
it's caught and then unexpectedly logged later.

Change-Id: I040f7c7e5062672356000a1c50c4da2e857a7cbc
Merge "Don't log TRACE info in notify_about_instance_usage"