test/runtests.sh: add dmesg check

Lifted this from blktests, basically it just checks for known patterns
of kernel complaints. If we trigger one while running a test, we fail
the test case.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/.gitignore b/.gitignore
index fee76e8..48964d1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -88,6 +88,7 @@
 /test/timeout
 /test/timeout-overflow
 /test/config.local
+/test/*.dmesg
 
 config-host.h
 config-host.mak