Add db route

[tengattack]

Add db route allow db level routing.

For example, this can limit database node2_db queries to node2 only:

schema_list :
-
    user: root
    nodes: [node1,node2]
    default: node1
    shard:
    -
        db : node2_db
        nodes: [node2]

[shrhawk-entertainer]

@tengattack does this support table also?
for example, want to route some tables to a specific node not based on hash or range types

[tengattack]

@tengattack did this support table also?
for example, want to route some tables to a specific node not based on hash or range types

Sorry, it only supports in database level now.