DERBY-6509 Convert lang/currentSchema.sql to JUnit CurrentSchemaTest

Patch derby-6509-1 which converts the test and wires in and out of
the JUnit and harness test suites respectively.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1579759 13f79535-47bb-0310-9956-ffa450edef68