Explicilty disabled JAI's native media lib for unit tests in import/core

Explicitly disable use of JAI's native media library even if it's present.
* Pros
 * The JAI media lib implementation distributed with OS X has an issue causing the unit test to fail, this is resolved
     * _The JAI in OS X is embedded in the JRE and overrides the version specified in maven_
 * Will allow for consistent unit test results across all platforms using the same version of JAI
 * Will avoid informational exception stack trace with error loading mlib classes during unit tests (no broken windows!)
* Cons
  * Won't test use of JAI media lib if present
 
Notes
* Plugin version specification could be pushed up to a parent and specified using plugin management section for consistent plugin versioning across all children.