RFR 8156931: java.nio.Buffer tests cleanup

[Pavel Rappo]

Hi,

Could you please review my change for JDK-8156931?

   http://cr.openjdk.java.net/~prappo/8156931/webrev.00/

It's a pass through before updating tests for "(bf) Hoist slice and duplicate
methods up to java.nio.Buffer"

   https://bugs.openjdk.java.net/browse/JDK-8150785

Thanks,
-Pavel