XDCR - P2P - show UI message while P2P is running

In a big cluster like system test, when starting XDCR pipeline that contains many nodes in a cluster, it'll mean a long P2P timeout (since P2P timeout is dependent upon the number of peer KV nodes in a cluster).

If one node is slow out of the whole cluster, then it could mean that many nodes are waiting for the one slow node to respond and no replication is taking place. There is no UI feedback to tell the user that this is happening, and from a stats perspective nothing is moving.

It'll be good to show a message telling the user that P2P is running so no data movement is taking place yet ... without needing to dig into the logs before they think replication is broken.