Fix for Guava and jclouds issue #1196

It looks as though Guava has fixed this with their patch release 16.0.1 and jclouds are going to simply rely on this update in upcoming 1.6.4 and 1.7.1 patch releases, so we simply upgrade the Guava version and depend on it directly, while excluding the old version when provided elsewhere.

Note that this upgrade **removes** the deprecated method `Closeables#closeQuietly(Closeable)` from Guava. The jclouds code in _1.7.1-SNAPSHOT_ simply re-adds a `Closeables2` class with the missing method; this idiom matches previous updates involving removal of deprecated code. For Brooklyn we can simply replace all occurrences with this stream utility method instead:

    brooklyn.util.stream.Streams#closeQuietly(Closeable)