fix VAE loading issue in train_dreambooth (#7632)

* fixed vae loading issue #7619

* rerun make style && make quality

* bring back model_has_vae and add change \ to / in config_file_name on windows os to make match work

* add missing import platform

* bring back import model_info

* make config_file_name OS independent

* switch to using Path.as_posix() to resolve OS dependence

* improve style

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Co-authored-by: Sayak Paul <spsayakpaul@gmail.com>
Co-authored-by: bssrdf <bssrdf@gmail.com>
Co-authored-by: Dhruv Nair <dhruv.nair@gmail.com>

examples/dreambooth/train_dreambooth.py

@@ -759,7 +759,7 @@ class PromptDataset(Dataset):
 
 
 def model_has_vae(args):
-    config_file_name = os.path.join("vae", AutoencoderKL.config_name)
+    config_file_name = Path("vae", AutoencoderKL.config_name).as_posix()
     if os.path.isdir(args.pretrained_model_name_or_path):
         config_file_name = os.path.join(args.pretrained_model_name_or_path, config_file_name)
         return os.path.isfile(config_file_name)