Replication can be enabled and started without a connection [JIRA: RIAK-2234]

[jcapricebasho]

In a standard replication setup, the below commands would be run:

riak-repl clustername <clustername>
riak-repl connect <ip>:<port>
riak-repl realtime enable <sink_clustername>
riak-repl realtime start <sink_clustername>
riak-repl fullsync enable <sink_clustername>
riak-repl fullsync start <sink_clustername>

However, if you do not run riak-repl connect <ip>:<port>, the following commands to enable and start both realtime and fullsync replication succeed and return no error. The commands do not appear to be no-op commands as well, as a realtime queue is started and will fill up with objects to be replicated to the specified unconnected sink.

We should make these commands no-ops when no sink clusters are connected, and alert the user when running enables and starts.

Here is an example riak-repl status after running the above commands without riak-repl connect <ip>:<port>:

realtime_enabled: "test2"
realtime_started: "test2"
fullsync_enabled: "test2"
fullsync_running: []
proxy_get_enabled: []
server_bytes_sent: 0
server_bytes_recv: 0
server_connects: 0
server_connect_errors: 0
server_fullsyncs: 0
client_bytes_sent: 0
client_bytes_recv: 0
client_connects: 0
client_connect_errors: 0
client_redirect: 0
objects_dropped_no_clients: 0
objects_dropped_no_leader: 0
objects_sent: 0
objects_forwarded: 0
elections_elected: 0
elections_leader_changed: 0
client_rx_kbps: [0,0,0,0,0,0,0,0]
client_tx_kbps: [0,0,0,0,0,0,0,0]
server_rx_kbps: [0,0,0,0,0,0,0,0]
server_tx_kbps: [0,0,0,0,0,0,0,0]
rt_source_errors: 0
rt_sink_errors: 0
rt_dirty: 0
leader: undefined
local_leader_message_queue_len: 0
local_leader_heap_size: 233
client_stats: []
sinks: []
sources: [{source_stats,
              [{pid,"<0.9343.0>"},
               {message_queue_len,0},
               {rt_source_connected_to,
                   [{sink,"test2"},{pid,"<0.9343.0>"},{connected,false}]}]}]
fullsync_coordinator: [{"test2",
                        [{cluster,"test2"},
                         {queued,0},
                         {in_progress,0},
                         {waiting_for_retry,0},
                         {starting,0},
                         {successful_exits,0},
                         {error_exits,0},
                         {retry_exits,0},
                         {soft_retry_exits,0},
                         {busy_nodes,0},
                         {last_running_refresh,{{2015,10,22},{15,52,47}}},
                         {running_stats,[]},
                         {socket,[]},
                         {fullsyncs_completed,0},
                         {last_fullsync_started,undefined},
                         {last_fullsync_duration,undefined},
                         {last_fullsync_completed,undefined},
                         {fullsync_suggested,[]},
                         {fullsync_suggested_during_fs,[]}]}]
fullsync_coordinator_srv: []
cluster_name: <<"test">>
cluster_leader: '[email protected]'
connected_clusters: [<<"test2">>]
realtime_queue_stats: [{percent_bytes_used,0.001},
                       {bytes,760},
                       {max_bytes,104857600},
                       {consumers,[{"test2",
                                    [{pending,0},
                                     {unacked,0},
                                     {drops,0},
                                     {errs,0}]}]},
                       {overload_drops,0}]
proxy_get: [{requester,[]},{provider,[]}]
realtime_send_kbps: 0
realtime_recv_kbps: 0
fullsync_send_kbps: 0
fullsync_recv_kbps: 0