JCLOUDS-650: ContainerNotFoundException on putBlob

Found with Ceph s3-tests and s3proxy.
JCLOUDS-652: Require JDK 7

Moving to Java 7 allows jclouds to use more language and library
features such as try-with-resources and HTTP client improvements.
JCLOUDS-264: Allow payloads greater than 2 GB

Enabled by JDK 7.