redis: Add username

Redis introduced ACL feature in 4.0.0, and this feature is supported by
redis-py since 3.4.0[1]. When ACL is enabled, authentication requires
username in addition to password.

[1] 8df8cd54d1

Change-Id: I9b53c3a314dcffbe49535799ba6d7a1fdddb8d84

setup.cfg

@@ -53,7 +53,7 @@ etcd3gw =
 zake =
   zake>=0.1.6 # Apache-2.0
 redis =
-  redis>=3.1.0 # MIT
+  redis>=3.4.0 # MIT
 postgresql =
   psycopg2>=2.5 # LGPL/ZPL
 mysql =

tooz/drivers/redis.py

@@ -159,7 +159,8 @@ class RedisDriver(coordination.CoordinationDriverCachedRunWatchers,
 
     The Redis driver connection URI should look like::
 
-      redis://[:PASSWORD@]HOST:PORT[?OPTION=VALUE[&OPTION2=VALUE2[&...]]]
+      redis://[USERNAME:PASSWORD@]HOST:PORT
+          [?OPTION=VALUE[&OPTION2=VALUE2[&...]]]
 
     For a list of options recognized by this driver, see the documentation
     for the member CLIENT_ARGS, and to determine the expected types of those
@@ -428,6 +429,8 @@ return 1
             if not parsed_url.path:
                 raise ValueError("Expected socket path in parsed urls path")
             kwargs['unix_socket_path'] = parsed_url.path
+        if parsed_url.username:
+            kwargs['username'] = parsed_url.username
         if parsed_url.password:
             kwargs['password'] = parsed_url.password
         for a in cls.CLIENT_ARGS: