selftests: ftrace: Add --quiet option not to show error logs on screen

selftests: ftrace: Add --quiet option not to show error logs on screen

Since the verbose error logs scrolls out previous test results
--quiet option suppress to show such message.

e.g.
 # ./ftracetest -q
=== Ftrace unit tests ===
[1] Basic trace file check	[PASS]
[2] Basic test for tracers	[PASS]
[3] Basic trace clock test	[PASS]
[4] Basic event tracing check	[PASS]
[5] event tracing - enable/disable with event level files	[PASS]
[6] event tracing - restricts events based on pid	[PASS]
[7] event tracing - enable/disable with subsystem level files	[PASS]
[8] event tracing - enable/disable with top level files	[PASS]
[9] ftrace - function graph filters with stack tracer	[UNSUPPORTED]
[10] ftrace - function graph filters	[UNSUPPORTED]
[11] ftrace - function profiler with function tracing	[UNSUPPORTED]
[12] Test creation and deletion of trace instances while setting an event
	[PASS]
[13] Test creation and deletion of trace instances	[PASS]
[14] Kprobe dynamic event - adding and removing	[UNSUPPORTED]
[15] Kprobe dynamic event - busy event check	[UNSUPPORTED]
[16] Kprobe dynamic event with arguments	[UNSUPPORTED]
[17] Kprobe dynamic event with function tracer	[UNSUPPORTED]
[18] Kretprobe dynamic event with arguments	[UNSUPPORTED]
[19] event trigger - test event enable/disable trigger	[PASS]
[20] event trigger - test trigger filter	[PASS]
[21] event trigger - test histogram modifiers	[UNSUPPORTED]
[22] event trigger - test histogram trigger	[UNSUPPORTED]
[23] event trigger - test multiple histogram triggers	[UNSUPPORTED]
[24] event trigger - test snapshot-trigger	[FAIL]
[25] event trigger - test stacktrace-trigger	[PASS]
[26] event trigger - test traceon/off trigger	[PASS]

# of passed:  14
# of failed:  1
# of unresolved:  0
# of untested:  0
# of unsupported:  11
# of xfailed:  0
# of undefined(test bug):  0

Link: http://lkml.kernel.org/r/147928399712.22982.8284640390982775052.stgit@devbox
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>