rpc/rpcstatus: add status codes for DeleteObjects

This change introduces RPC status codes representing the various
reasons that the DeleteObjects operation may fail:

- DeleteObjectsNoItems
- DeleteObjectsTooManyItems

While the following new status codes are also used by DeleteObjects,
they represent generic failures. New metainfo endpoints are encouraged
to use them as well:

- BucketNameMissing
- BucketNameInvalid
- ObjectKeyMissing
- ObjectKeyTooLong
- ObjectVersionInvalid
- BucketNotFound

References storj/edge#516
References storj/edge#521

Change-Id: Ia0ee491d67bddb43d5999bed466f4c9e16422d6c

Author: jewharton

rpc/rpcstatus/status.go

@@ -41,6 +41,14 @@ const (
 	Unauthenticated    StatusCode = 16
 	MethodNotAllowed   StatusCode = 17
 
+	BucketNameMissing    StatusCode = 10014
+	BucketNameInvalid    StatusCode = 10015
+	ObjectKeyMissing     StatusCode = 10016
+	ObjectKeyTooLong     StatusCode = 10017
+	ObjectVersionInvalid StatusCode = 10018
+
+	BucketNotFound StatusCode = 10019
+
 	ObjectLockEndpointsDisabled                      StatusCode = 10000
 	ObjectLockDisabledForProject                     StatusCode = 10001
 	ObjectLockInvalidBucketState                     StatusCode = 10002
@@ -56,6 +64,9 @@ const (
 
 	PlacementInvalidValue      StatusCode = 10012
 	PlacementConflictingValues StatusCode = 10013
+
+	DeleteObjectsNoItems      StatusCode = 10020
+	DeleteObjectsTooManyItems StatusCode = 10021
 )
 
 // Code returns the status code associated with the error.