selftests/ftrace: Add error_log testcase for probe errors

Add error_log testcase for error logs on probe events.
This tests most of error cases and checks the error position
is correct.

Link: http://lkml.kernel.org/r/63d695b74e0965988fa54ffa12beeb2c3475250d.1554072478.git.tom.zanussi@linux.intel.com

Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
[tom.zanussi@linux.intel.com: changed >& redirection to 2>]
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>