qemu-iotests: Fail test if explicit test case number is unknown

When we expand a number range, we just print "$id - unknown test,
ignored", this is convenient if we want to run a range of tests.

When we designate a test case number explicitly, we shouldn't just
ignore it if the case script doesn't exist.

Print an error and fail the test.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/common

@@ -376,10 +376,16 @@ BEGIN        { for (t='$start'; t<='$end'; t++) printf "%03d\n",t }' \
                     echo $id >>$tmp.list
                 else
                     # oops
-                    echo "$id - unknown test, ignored"
+                    if [ "$start" == "$end" -a "$id" == "$end" ]
+                    then
+                        echo "$id - unknown test"
+                        exit 1
+                    else
+                        echo "$id - unknown test, ignored"
+                    fi
                 fi
             fi
-        done
+        done || exit 1
     fi
 
 done