JCLOUDS-534: Upgrade to Guava 17.0

Release notes:

https://code.google.com/p/guava-libraries/wiki/Release17
JCLOUDS-505: Remove unused ObjectMD5

The only users of this seem to be
org.jclouds.atmos.blobstore.strategy.FindMD5InUserMetadata and
org.jclouds.azureblob.blobstore.strategy.FindMD5InBlobProperties which
are themselves unused.