Restore {ok, Docs} from get_design_docs
Skip ddoc pull, use middleman for validation reset

We were pulling a list of design documents and then ignoring the result
when the #db was a partition of a clustered database.  Also, the call to
fabric:reset_validation_funs/1 can occasionally cause a stray rexi_EXIT
message to arrive in the db_updater mailbox (and subsequently kill the
server) if a worker fails.  I don't think that's desired behavior,
though it's a debatable point.  This patch spawns a middleman process to
act as a sink for those stray messages.

BugzID: 13087