tests: always check expected results as text, not binary

Even if we get \0 in results, we want to see the output, not helpful
"binary files differ" messages.

Signed-off-by: Nick Alcock <nick.alcock@oracle.com>

runtest.sh

@@ -506,7 +506,7 @@ resultslog()
         elif [[ -n $want_expected_diff ]]; then
             log "Diff against expected:\n"
 
-            diff -u $rfile $tmpdir/test.out | tee -a $LOGFILE >> $SUMFILE
+            diff -au $rfile $tmpdir/test.out | tee -a $LOGFILE >> $SUMFILE
         fi
     fi