JDK 1.7 Support Added

* Updated build.xml files with 1.6 source and target values.
  We currently compile using the 1.7 compiler, but only support
  1.6 language features. (Used JDK 1.7 patch provided by agrimm)

* Updated JDK checking in eucalyptus-cloud init script.

* Updated Java versions in configure script.

* Updated INSTALL documentation to refer to JDK 1.7 packages.