trace-cmd: Only show unit test output when -v is supplied

The "Use libraries to read file" test shows the output of the reading of
the trace.dat file. That should only happen if the '-v' option is
supplied, otherwise, it should be muted.

Link: https://lore.kernel.org/linux-trace-devel/20221115205355.2580214-3-rostedt@goodmis.org

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>