Relocate test-only REST "client" from src/ to test/ and mark Private

Relocate test-only REST "client" from src/ to test/ and annotate as Private. The classes o.a.h.h.rest.Remote* were developed to facilitate REST unit tests and incorrectly committed to src/ .

Although this "breaks" compatibility by moving public classes to test jar and marking them private, no attention has been paid to these classes with respect to performance, convenience, or security. Consensus from various discussions over the years is to move them to test/ as was intent of the original committer, but misplaced by the same individual.