Revert JCLOUDS-652 so that we don't require java 7

This reverts the change that required users to use java language 7.
https://issues.apache.org/jira/browse/JCLOUDS-652

This takes care of the default http driver and single-shot 2GB fixed length posts. Basically, those using JRE7 will work. Those not, can choose a different http driver.
https://issues.apache.org/jira/browse/JCLOUDS-264

Note: this also permits special casing of modules that need Java 7. For example, the filesystem api is configured so that if the JRE is at least 7, it will build.

Ex. This is really about what this class supports. More of an interest wrt android (although still uploading >2GB in one shot is dubious and I'm really surprised we've still not started or landed the MPU tool!)