rados.h: use macros to generate osd ops definitons and strings

Eliminate multiple points of maintenance by using macros - no
functional changes apart from adding strings which were missing.

Signed-off-by: Ilya Dryomov <idryomov@redhat.com>
Merge pull request #2646 from ceph/wip-osd-op-macro

rados.h: use macros to generate osd ops definitons and strings

Reviewed-by: Sage Weil <sage@redhat.com>