UBUNTU: SAUCE: selftests/ftrace: Use printf instead of echo in kprobe syntax error...

UBUNTU: SAUCE: selftests/ftrace: Use printf instead of echo in kprobe syntax error tests

Test cases which use echo to write strings containing backslashes
fail with some shells, as echo's treatment of backslashes in
strings varies between shell implementations. Use printf instead,
as it should behave consistently across different shells. This
requires adjustments to the strings to escape \ and % characters.
ftrace_errlog_check() must also re-escape these characters after
processing them to remove ^ characters.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>