selftests/ftrace: Move kprobe/uprobe check_error() to test.d/functions

The k/uprobe_sytax_errors test case defines a check_error() function
used to run a command and check the position of the caret in the
output.

This would be useful for other ftrace facilities too, so move it to
test.d/functions for use by anyone.  In the process, rename it to
ftrace_errlog_check() and parametrize it for general use.

Link: http://lkml.kernel.org/r/9f88080a06f1755811f69081926afe7e5cb53178.1554072478.git.tom.zanussi@linux.intel.com

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>