PoC: Patroni on pure RAFT (#375)

* new node can join the cluster dynamically and become a part of consensus
 * it is also possible to join only Patroni cluster (without adding the node to the raft), just comment or remove `raft.self_addr` for that
 * when the node joins the cluster it is using values from `raft.partner_addrs` only for initial discovery.
* It is possible to run Patroni and Postgres on two nodes plus one node with `patroni_raft_controller` (without Patroni and Postgres). In such setup one can temporarily lose one node without affecting the primary.

setup.py

@@ -23,7 +23,7 @@ KEYWORDS = 'etcd governor patroni postgresql postgres ha haproxy confd' +\
     ' zookeeper exhibitor consul streaming replication kubernetes k8s'
 
 EXTRAS_REQUIRE = {'aws': ['boto'], 'etcd': ['python-etcd'], 'consul': ['python-consul'],
-                  'exhibitor': ['kazoo'], 'zookeeper': ['kazoo'], 'kubernetes': []}
+                  'exhibitor': ['kazoo'], 'zookeeper': ['kazoo'], 'kubernetes': [], 'raft': ['pysyncobj']}
 COVERAGE_XML = True
 COVERAGE_HTML = False
 
@@ -51,6 +51,7 @@ CLASSIFIERS = [
 
 CONSOLE_SCRIPTS = ['patroni = patroni:main',
                    'patronictl = patroni.ctl:ctl',
+                   'patroni_raft_controller = patroni.raft_controller:main',
                    "patroni_wale_restore = patroni.scripts.wale_restore:main",
                    "patroni_aws = patroni.scripts.aws:main"]