trace/simple: Enable tracing on startup only if the user specifies a trace option

trace/simple: Enable tracing on startup only if the user specifies a trace option

Tracing can be enabled at the command line or via the
monitor. Command-line trace options are recorded during
trace_opt_parse(), but tracing is not enabled until the various
front-ends later call trace_init_file(). If the user passes a trace
option on the command-line, remember that and enable tracing during
trace_init_file().  Otherwise, trace_init_file() should record the
trace file specified by the frontend and avoid enabling traces
until the user requests them via the monitor.

This fixes 1b7157be3a8c4300fc8044d40f4b2e64a152a1b4 and also
db25d56c014aa1a96319c663e0a60346a223b31e, by allowing the user
to enable traces on the command line and also avoiding
unwanted trace-<pid> files when the user has not asked for them.

Fixes: 1b7157be3a8c4300fc8044d40f4b2e64a152a1b4
Signed-off-by: Josh DuBois <josh@joshdubois.com>
Message-id: 20200816174610.20253-1-josh@joshdubois.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>