tests: df: check that -k and -m are supported

* tests/df/df-output.sh: Check that the block size is correct when using
-k and -m.

tests/df/df-output.sh

@@ -98,6 +98,24 @@ sed -e '1 {
         }' out > out2
 compare exp out2 || fail=1
 
+df -k --output=size '.' >out || fail=1
+sed -e '1 {
+          s/ *//
+          q
+        }' out > out2
+compare exp out2 || fail=1
+
+cat <<\EOF > exp || framework_failure_
+1M-blocks
+EOF
+
+df -m --output=size '.' >out || fail=1
+sed -e '1 {
+          s/ *//
+          q
+        }' out > out2
+compare exp out2 || fail=1
+
 # Ensure that the grand total line now contains a "-" in the TARGET field ...
 cat <<\EOF > exp || framework_failure_
 -