signature: Region changes should be handled just like AWS. (#2805)

- PutBucket happens with 'us-east-1'.
- ListBuckets happens with any region.
- GetBucketLocation happens with 'us-east-1' and location is returned.

cmd/auth-handler_test.go

@@ -294,7 +294,7 @@ func TestIsReqAuthenticated(t *testing.T) {
 		if testCase.s3Error == ErrBadDigest {
 			testCase.req.Header.Set("Content-Md5", "garbage")
 		}
-		if s3Error := isReqAuthenticated(testCase.req); s3Error != testCase.s3Error {
+		if s3Error := isReqAuthenticated(testCase.req, serverConfig.GetRegion()); s3Error != testCase.s3Error {
 			t.Fatalf("Unexpected s3error returned wanted %d, got %d", testCase.s3Error, s3Error)
 		}
 	}