XD-1413, XD-1385 Create spring-xd-test fixtures, JDBC Acceptance Tests

 - Also moved fixture code from test to main in the spring-shell project.
 - Removed unnecessary checks from JDBC Init
 - Removed JDBCTestSupport.
 - JDBCSink now offers a isReady method that can be called to verify if the connection is valid.  True if it is valid.  False if invalid.
 - JDBC tests will throw an exception if can't connect to database.  Where before it would ignore the test.
 - Moved all fixtures to spring-xd-test-fixtures project.
    - Updated dependencies accordingly.
    - Ran Sonar to verify no package tangles.  (MLP - need to rerun after my changes)
 - Created SimpleHttpSource for acceptance tests that sends http posts without using any of the XD Shell utils.