replication: recfg with 0 quorum returns immediately

Replication quorum 0 not only affects orphan status, but also,
according to documentation, makes box.cfg() return immediately
regardless of whether connections to upstreams are established.

It was not so before the patch. What is worse, even with non 0
quorum the instance was blocked on reconfiguration for connect
timeout seconds, if at least one node is not connected.

Now quorum is respected on reconfiguration. On a bootstrap it is
still impossible to return earlier than
replication_connect_timeout, because nodes need to choose some
cluster settings. Too early start would make it impossible -
cluster's participants will just start and choose different
cluster UUIDs.

Closes #3760

(cherry picked from commit c6bea65f)