8181867: [tests] Reorganize EchoHandlers Summary: This fix reorganize some test files and rename some test classes. Several classes named EchoHandler in the unnamed package are renamed to make it clear what classes (and sources) tests that use these EchoHandler implementations effectively depend on. Reviewed-by: chegar

^build/
^dist/
^.idea/
nbproject/private/
^webrev
^.src-rev$
^.jib/
.DS_Store
.metadata/
.recommenders/