tests: add ZZ_check_dmesg

This way the testsuit automatically fails if we hit a DRM_ERROR
or a WARN/BUG somewhere.

... i.e. this is the Jesse Barnes catcher ...

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

tests/ZZ_check_dmesg

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+if dmesg | grep '\*ERROR\*'  > /dev/null ; then
+	echo "DRM_ERROR dirt in dmesg"
+	exit 1
+fi
+
+if dmesg | grep -- '------\[ cut here \]----' > /dev/null  ; then
+	echo "found a backtrace in dmesg"
+	exit 1
+fi