FIX: Setting client options fails with "Server went away"

[patricknelson]

When defining a client prefix option for phpredis, there would be an exception Uncaught RedisException: Redis server went away. It looks like this was caused by calling $redis->setOption(Redis::OPT_PREFIX, 'foobar:') before the server connection in $redis->connect(...) was done.

Example configuration:

SS_Cache::add_backend('primary_redis', 'Redis', [
	'server' => [
		'host' => '127.0.0.1,
	],
	'client' => [
		// 👇 Results in an exception.
		'prefix' => 'foobar:',
	],
]);

This pull request just relocates the server config above the client configuration so that setting the prefix will work.