Implemented allowlist for REST API (#1959)

If configured, only IPs that matching rules would be allowed to call unsafe endpoints.
In addition to that, it is possible to automatically include IPs of members of the cluster to the list.
If neither of the above is configured the old behavior is retained.

Partially address https://github.com/zalando/patroni/issues/1734

setup.py

@@ -24,7 +24,7 @@ KEYWORDS = 'etcd governor patroni postgresql postgres ha haproxy confd' +\
 
 EXTRAS_REQUIRE = {'aws': ['boto'], 'etcd': ['python-etcd'], 'etcd3': ['python-etcd'],
                   'consul': ['python-consul'], 'exhibitor': ['kazoo'], 'zookeeper': ['kazoo'],
-                  'kubernetes': ['ipaddress'], 'raft': ['pysyncobj', 'cryptography']}
+                  'kubernetes': [], 'raft': ['pysyncobj', 'cryptography']}
 COVERAGE_XML = True
 COVERAGE_HTML = False
 
@@ -175,13 +175,12 @@ def setup_package(version):
         for e, deps in EXTRAS_REQUIRE.items():
             for i, v in enumerate(deps):
                 if r.startswith(v):
-                    if e != 'kubernetes' or sys.version_info < (3, 0, 0):
-                        deps[i] = r
-                    else:
-                        deps = []
+                    deps[i] = r
                     EXTRAS_REQUIRE[e] = deps
                     extra = True
                     break
+            if extra:
+                break
         if not extra:
             install_requires.append(r)