This is the last commit of the series, in which we enforce
publishing of external endpoints to peers of different orgs
 and publishing of both external and internal endpoints only
 within the peer's organization.

The commit addesses this only in the gossip layer,
as the discovery layer has been taken care of in previous commits.

It contains a test in which we:
- Create 2 orgs with 5 peers each, while the first 2 peers have external
  endpoints, and the rest don't.
- The first org has a bootstrap peer, the second doesn't.
- JoinChannel is invoked with the first peer of each org as anchor peers.
- It is tested that:
  - Peers know peers from other orgs only if they both
    have external endpoints.
  - Peers do not know the internal endpoints of peers of other orgs.

Change-Id: I157c8cea29b35adb84314fcb695413b005f2b236
Signed-off-by: Yacov Manevich <yacovm@il.ibm.com>