export Sentinel at the top level and expose SSL the same way as Redis

Now that `Sentinel` needs to be used specifically instead of via
`Redis`, this change exports the class at the top level like the `Redis`
client is, and also allows the shorthand of `ssl=True` to set the
connection class to the `SentinelManagedSSLConnection`.

Author: terencehonles

README.md

@@ -365,14 +365,26 @@ Connecting redis-py to the Sentinel instance(s) is easy. You can use a
 Sentinel connection to discover the master and slaves network addresses:
 
 ``` pycon
->>> from redis.sentinel import Sentinel
+>>> from redis import Sentinel
 >>> sentinel = Sentinel([('localhost', 26379)], socket_timeout=0.1)
 >>> sentinel.discover_master('mymaster')
 ('127.0.0.1', 6379)
 >>> sentinel.discover_slaves('mymaster')
 [('127.0.0.1', 6380)]
 ```
 
+To connect to a sentinel which uses SSL ([see SSL
+connections](#ssl-connections) for more examples of SSL configurations):
+
+``` pycon
+>>> from redis import Sentinel
+>>> sentinel = Sentinel([('localhost', 26379)],
+                        ssl=True,
+                        ssl_ca_certs='/etc/ssl/certs/ca-certificates.crt')
+>>> sentinel.discover_master('mymaster')
+('127.0.0.1', 6379)
+```
+
 You can also create Redis client connections from a Sentinel instance.
 You can connect to either the master (for write operations) or a slave
 (for read-only operations).

redis/__init__.py

@@ -6,6 +6,12 @@
     SSLConnection,
     UnixDomainSocketConnection
 )
+from redis.sentinel import (
+    Sentinel,
+    SentinelConnectionPool,
+    SentinelManagedConnection,
+    SentinelManagedSSLConnection,
+)
 from redis.utils import from_url
 from redis.exceptions import (
     AuthenticationError,
@@ -51,6 +57,10 @@ def int_or_str(value):
     'Redis',
     'RedisError',
     'ResponseError',
+    'Sentinel',
+    'SentinelConnectionPool',
+    'SentinelManagedConnection',
+    'SentinelManagedSSLConnection',
     'SSLConnection',
     'StrictRedis',
     'TimeoutError',

redis/sentinel.py

@@ -80,7 +80,9 @@ class SentinelConnectionPool(ConnectionPool):
 
     def __init__(self, service_name, sentinel_manager, **kwargs):
         kwargs['connection_class'] = kwargs.get(
-            'connection_class', SentinelManagedConnection)
+            'connection_class',
+            SentinelManagedSSLConnection if kwargs.pop('ssl', False)
+            else SentinelManagedConnection)
         self.is_master = kwargs.pop('is_master', True)
         self.check_connection = kwargs.pop('check_connection', False)
         super().__init__(**kwargs)