trace-cmd: Do not enable tracing until exec
trace-cmd: Do not enable tracing until exec

Wait till the last moment to enable tracing. Otherwise we trace
the trace-cmd utility setting up the program and waste a lot of
the data file.

Signed-off-by: Steven Rostedt <43232e92d70cc7aa53504ad0397085ee47bad87f@goodmis.org>

bigzz/trace-cmd,bigzz/trace-cmd