ktest: Add INGORE_ERRORS to ignore warnings in boot up

When testing a kernel that has warnings, ktest.pl will fail the test
when it sees the warning. If you need to test the the kernel and want
to ignore the errors that are produced, the option IGNORE_ERRORS has
been added. When IGNORE_ERRORS is set to something other than 0, it will
ignore call traces due to WARN_ON().

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