support get region by id

[siddontang]

now we only support get region by key, I think sometimes we may need get region by region id too.
If support, we should add a proto in pdpb.proto, maybe in GetMeta is OK, like

message GetMetaRequest {
    optional MetaType meta_type    = 1;
    optional uint64 node_id        = 2;
    optional uint64 store_id       = 3;
    optional bytes region_key      = 4;
    optional uint64 cluster_id     = 5;
    optional uint64 region_id    = 6;
}

If the meta_type is Region and region_key is set, we will use get region, or else region_id is set, we will use get region by id.

@qiuyesuifeng

[qiuyesuifeng]

Agreed, but should we add a variable like type to show whether get region by id or key?

[siddontang]

maybe no need, because they return same value, a region meta.

[qiuyesuifeng]

Is it necessary to do this? Seems we have not used it now.
@siddontang

[qiuyesuifeng]

No need now, close it.