[BUILD] Fix for false positives reported by mima on PR 2194.

Actually false positive reported was due to mima generator not picking up the new jars in presence of old jars(theoretically this should not have happened.). So as a workaround, ran them both separately and just append them together.
I don't see the `args` array being used in GenerateMIMAIgnore.scala, where are the "new" and "old" arguments being used anywhere?