ACCUMULO-2010 Remove Closeable from interfaces

  This gets around compiler warnings about resource leaks. This reverts
  back to the old API semantics, where we are not advising that clients
  close Instance objects. If it is determined in the future that we
  should be advising clients to do this, and therefore want to
  re-introduce the Closeable interface to Instance and the ZooKeeper
  objects, it should be accompanied by changes that actually close these
  resources in our own code. We should not be recommending this without
  following our own recommendation, and adding Closeable to the
  interface is a recommendation to call the close method.

  Also clean up additional resource warnings.