Fix profiling endpoint and adding tests (#1917)

Signed-off-by: Lenin Alevski <alevsk.8772@gmail.com>

restapi/admin_profiling.go

@@ -118,8 +118,7 @@ func stopProfiling(ctx context.Context, client MinioAdmin) (io.ReadCloser, error
 
 // getProfilingStopResponse() performs setPolicy() and serializes it to the handler's output
 func getProfilingStopResponse(session *models.Principal) (io.ReadCloser, *models.Error) {
-	ctx, cancel := context.WithCancel(context.Background())
-	defer cancel()
+	ctx := context.Background()
 	mAdmin, err := NewMinioAdminClient(session)
 	if err != nil {
 		return nil, prepareError(err)