Always stop tracing before starting tracing, for greater reliability
Always stop tracing before starting tracing, for greater reliability

If you start ETW tracing when it is already running then you get error
messages that are slightly cryptic:

xperf: error: NT Kernel Logger: Cannot create a file when that file already exists. (0xb7).

Hmmm. Not obvious what the problem is. So, now I force-stop tracing
before starting it. This avoids a cryptic error message and avoids an
otherwise latent failure possibility - previously if you *ever* forgot
to run stop_tracing.bat then your lab tracing could end up broken until
you rebooted.

google/UIforETW,google/UIforETW,mwinterb/UIforETW,google/UIforETW,MikeMarcin/UIforETW,ariccio/UIforETW,ariccio/UIforETW,mwinterb/UIforETW,ariccio/UIforETW,google/UIforETW,MikeMarcin/UIforETW,MikeMarcin/UIforETW,ariccio/UIforETW,mwinterb/UIforETW