ktest: Ignore errors it tests if IGNORE_ERRORS is set

The option IGNORE_ERRORS is used to allow a test to succeed even if a
warning appears from the kernel. Sometimes kernels will produce warnings
that are not associated with a test, and the user wants to test
something else.

The IGNORE_ERRORS works for boot up, but was not preventing test runs to
succeed if the kernel produced a warning.

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