Fix import if PyTorch is not installed (#715)

* Fix import if PyTorch is not installed.

* Style (blank line)

Author: pcuenca

src/diffusers/utils/__init__.py

@@ -37,7 +37,10 @@
 )
 from .logging import get_logger
 from .outputs import BaseOutput
-from .testing_utils import floats_tensor, load_image, parse_flag_from_env, slow, torch_device
+
+
+if is_torch_available():
+    from .testing_utils import floats_tensor, load_image, parse_flag_from_env, slow, torch_device
 
 
 logger = get_logger(__name__)