Refactoring volume server options.
Refactoring volume server options.

chrislusf/seaweedfs,hxiaodon/seaweedfs,hxiaodon/seaweedfs,chrislusf/seaweedfs,k85169336/seaweedfs,chrislusf/seaweedfs,chrislusf/seaweedfs,k85169336/seaweedfs