should be able to grow and shrink memcache buckets

Currently, if a cache bucket is defined, the size cannot be changed without deleting and recreating it. This makes certain use cases pretty difficult. For instance:

Assume that there are two buckets in the cluster.
bucket A - 1000MB (90% space is used, currently)
bucket B - 1000MB (10% space is used, currently)

In the above case, the space of bucket A must be increased.
Adding more space on bucket A can be done by one of two methods.

1. Add a new node into the cluster.
2. Change the space of buckets like followings

• Decrease the space of bucket B to 500MB and then increase the space of bucket A to 1500MB.

The second approach is not currently possible.