delete bucket also removes collection data

weed/pb/filer.proto

@@ -30,6 +30,9 @@ service SeaweedFiler {
     rpc LookupVolume (LookupVolumeRequest) returns (LookupVolumeResponse) {
     }
 
+    rpc DeleteCollection (DeleteCollectionRequest) returns (DeleteCollectionResponse) {
+    }
+
 }
 
 //////////////////////////////////////////////////
@@ -153,3 +156,10 @@ message Location {
 message LookupVolumeResponse {
     map<string, Locations> locations_map = 1;
 }
+
+message DeleteCollectionRequest {
+    string collection = 1;
+}
+
+message DeleteCollectionResponse {
+}