librbd/deep_copy: added bitwise flag parameter to object copy

librbd/deep_copy: added bitwise flag parameter to object copy

This initial version subsumes the original "flatten" boolean flag.

Signed-off-by: Jason Dillaman <dillaman@redhat.com>
(cherry picked from commit e79f6b1c157e042f57b577bc510debb21e004ea7)

Conflicts:
	src/librbd/deep_copy/ImageCopyRequest.cc (FunctionContext vs LambdaContext, no handler param for ObjectCopyRequest)
	src/librbd/deep_copy/ObjectCopyRequest.cc
	src/librbd/deep_copy/ObjectCopyRequest.h
	src/librbd/io/CopyupRequest.cc
	src/librbd/operation/MigrateRequest.cc
	src/test/librbd/deep_copy/test_mock_ImageCopyRequest.cc
	src/test/librbd/deep_copy/test_mock_ObjectCopyRequest.cc
	src/test/librbd/io/test_mock_CopyupRequest.cc
                (no handler param for ObjectCopyRequest)