Fix --remote option to replication start

Declaring --remote as a 'Set<String>' field trips args4j's
Setters.create(), which only treats List, Map, and Arrays as
multi-value containers. Use a method-based @Option that adds
each --remote value into a Set<String> to work around this.

Change-Id: Ic4b4242f3c9ac05b822f2b62141ba34270619f70