Limit default redis max memory to 10GB. (#3630)

* Limit Redis max memory to 10GB/shard by default.

* Update stress tests.

* Reorganize

* Update

* Add minimum cap size for object store and redis.

* Small test update.

doc/source/index.rst

@@ -130,7 +130,6 @@ Ray comes with libraries that accelerate deep learning and reinforcement learnin
    fault-tolerance.rst
    plasma-object-store.rst
    resources.rst
-   redis-memory-management.rst
    tempfile.rst
 
 .. toctree::

doc/source/redis-memory-management.rst

@@ -1,12 +0,0 @@
-Redis Memory Management (Experimental)
-======================================
-
-Ray stores metadata associated with tasks and objects in one or more Redis
-servers, as described in `An Overview of the Internals
-<internals-overview.html>`_.  Applications that are long-running or have high
-task/object generation rate could risk high memory pressure, potentially leading
-to out-of-memory (OOM) errors.
-
-In Ray `0.6.1+` Redis shards can be configured to LRU evict task and object
-metadata by setting ``redis_max_memory`` when starting Ray. This supercedes the
-previously documented flushing functionality.