keystone.cache.redis config arguments url conflict host and port

[chuang]

version: 8.1.3.dev1
branch: stable/liberty

in my keystone.conf
```
[cache]
config_prefix = cache.keystone
expiration_time = 600
backend = dogpile.cache.redis
backend_argument = host:127.0.0.1
backend_argument = port:6380
backend_argument = db:0
```

Using this keystone.conf is not working.
```
2016-08-31 13:46:56.552 10387 CRITICAL keystone [-] AttributeError: 'list' object has no attribute 'decode'
2016-08-31 13:46:56.552 10387 ERROR keystone Traceback (most recent call last):
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/bin/keystone-wsgi-admin", line 34, in <module>
2016-08-31 13:46:56.552 10387 ERROR keystone server = wss.make_server('', args.port, initialize_admin_application())
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/keystone/server/wsgi.py", line 78, in initialize_admin_application
2016-08-31 13:46:56.552 10387 ERROR keystone return initialize_application('admin')
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/keystone/server/wsgi.py", line 64, in initialize_application
2016-08-31 13:46:56.552 10387 ERROR keystone startup_application_fn=loadapp)
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/keystone/server/common.py", line 49, in setup_backends
2016-08-31 13:46:56.552 10387 ERROR keystone drivers = backends.load_backends()
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/keystone/server/backends.py", line 33, in load_backends
2016-08-31 13:46:56.552 10387 ERROR keystone cache.configure_cache_region(cache.REGION)
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/keystone/common/cache/core.py", line 142, in configure_cache_region
2016-08-31 13:46:56.552 10387 ERROR keystone '%s.' % CONF.cache.config_prefix)
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/dogpile/cache/region.py", line 552, in configure_from_config
2016-08-31 13:46:56.552 10387 ERROR keystone "%swrap" % prefix, None),
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/dogpile/cache/region.py", line 417, in configure
2016-08-31 13:46:56.552 10387 ERROR keystone _config_prefix
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/dogpile/cache/api.py", line 81, in from_config_dict
2016-08-31 13:46:56.552 10387 ERROR keystone for key in config_dict
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/dogpile/cache/backends/redis.py", line 109, in __init__
2016-08-31 13:46:56.552 10387 ERROR keystone self.client = self._create_client()
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/dogpile/cache/backends/redis.py", line 129, in _create_client
2016-08-31 13:46:56.552 10387 ERROR keystone return redis.StrictRedis.from_url(**args)
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/redis/client.py", line 391, in from_url
2016-08-31 13:46:56.552 10387 ERROR keystone connection_pool = ConnectionPool.from_url(url, db=db, **kwargs)
2016-08-31 13:46:56.552 10387 ERROR keystone File "/home/chuangwang/.ostack/lib/python3.5/site-packages/redis/connection.py", line 774, in from_url
2016-08-31 13:46:56.552 10387 ERROR keystone url = urlparse(url)
2016-08-31 13:46:56.552 10387 ERROR keystone File "/usr/lib64/python3.5/urllib/parse.py", line 294, in urlparse
2016-08-31 13:46:56.552 10387 ERROR keystone url, scheme, _coerce_result = _coerce_args(url, scheme)
2016-08-31 13:46:56.552 10387 ERROR keystone File "/usr/lib64/python3.5/urllib/parse.py", line 114, in _coerce_args
2016-08-31 13:46:56.552 10387 ERROR keystone return _decode_args(args) + (_encode_result,)
2016-08-31 13:46:56.552 10387 ERROR keystone File "/usr/lib64/python3.5/urllib/parse.py", line 98, in _decode_args
2016-08-31 13:46:56.552 10387 ERROR keystone return tuple(x.decode(encoding, errors) if x else '' for x in args)
2016-08-31 13:46:56.552 10387 ERROR keystone File "/usr/lib64/python3.5/urllib/parse.py", line 98, in <genexpr>
2016-08-31 13:46:56.552 10387 ERROR keystone return tuple(x.decode(encoding, errors) if x else '' for x in args)
2016-08-31 13:46:56.552 10387 ERROR keystone AttributeError: 'list' object has no attribute 'decode'
2016-08-31 13:46:56.552 10387 ERROR keystone
```

Therefore, I view the code, find the reason.

Although I have not configured the `url` of `backend_argument`, the code sets the default `url` values `CONF.cache.memcache_servers`(file `keystone/common/cache/core.py`, line 112-113).

Therefore, the variable of `CONF.cache.memcache_servers` default value is `["localhost:11211"]`(file `keystone/common/config.py`, line 356-359).

So, when the code runs after `build_cache_conf` (file `keystone/common/cache/core.py`, line 139), the configuration of `cache` contain:
```
url = ["localhost:11211"]
host = "127.0.0.1"
port = 6380
db = 0
```

I use the cache backend `dogpile.cache.redis`, when the code is configured the `url` argument and creates `redis_client`, will use the function `StrictRedis.from_url` and `url` argument, and ignore the argument `host`,`port` and `db`.

If I will use the cache backend `dogpile.cache.redis`, I must configure the `keystone.conf`
```
[cache]
config_prefix = cache.keystone
expiration_time = 600
backend = dogpile.cache.redis
backend_argument = url:redis://192.168.7.51:6380/0
```

[Lance Bragstad (lbragstad)]

Keystone doesn't use these options directly. Instead, they are registered as options of the oslo.cache library [0]. Marking this as invalid since I think the fix, if any, would have to come from oslo.cache.

[0] https://github.com/openstack/oslo.cache/blob/cfe395f980603040ec40f9e6cf0a98a952f981ad/oslo_cache/_opts.py#L51-L55

[Lance Bragstad (lbragstad)]

Please feel free to reopen the issue if the problem resurfaces.