rgwlc: make invalid OpRule, lc_op_ctx accesses impossible

rgwlc: make invalid OpRule, lc_op_ctx accesses impossible

* At the cost of some additional overhead from deep copies,
  makes all access to these structures from WorkQ context safe.

* Lifts saved next-key-name and effective-mtime from LCOpAction
  to lc_op_ctx (via LCOpRule), former usage was incorrect

* Use ordered entry listing for Current, NonCurrent, and DM
  expiration--this is required by lookahead strategy

Signed-off-by: Matt Benjamin <mbenjamin@redhat.com>