tests/kernel/stackprot: 'fatal fault' is not a failure

By default, when a 'fatal fault' message is seen in the output of any
testcase, it is consider an inmediate fatal condition and the test
case is aborted.

However, this testcase is provoking the situation to verify the
condition is caught. This, it shall NOT be considered a fatal fault
and the default overriden to allow it to proceed.

This was done in the legacy testcases and now is moved to this
testcase, ported from legacy.

Change-Id: Icac6cf55cae2ffd9b071e9dd1f35918b7b30de5e
Signed-off-by: Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>