JCLOUDS-534: Upgrade to Guava 17.0

Release notes:

https://code.google.com/p/guava-libraries/wiki/Release17
Update pre-ASF copyright notices
Address Checkstyle violations
JCLOUDS-544: Add missing ERROR value to the Event.Status enum
Address checkstyle violations
Prefer Guava HttpHeaders over JAX-RS

jclouds code contains more instances of the former and Guava has
additional constants like CONTENT_MD5.
Make constants final classes instead of interfaces

This commit prohibits implementation of the empty interface and
instantiation of the class.  Refer to _Effective Java_ item 19 for
more background.
Incorrect constructor name
Migrate InputSupplier callers to ByteSource

A future version of Guava will remove InputSupplier.
Added unit tests for compute functions
JCLOUDS-543/JCLOUDS-572: Use slugs as IDs and assume a node can have a null image if it used an imageId that has been removed
Prefer Guava Files over FileInputStream

This ensures proper resource handling.
pull latest jclouds, it now includes our patch