[Blueprint] Prevent hidden artifacts parsing

Blueprint extension was parsing all files in the artifacts folder
including hidden files. This unwanted behavior can also raise errors
(eg. UnicodeDecodeError). This commit fixes this by preventing hidden
Linux and Windows files from being parsed.

closes #4984

src/blueprint/azext_blueprint/custom.py

@@ -7,6 +7,7 @@
 
 import json
 import os
+import stat
 from knack.util import CLIError
 from azure.cli.core.util import user_confirmation
 from azure.core.exceptions import HttpResponseError
@@ -48,12 +49,15 @@ def import_blueprint_with_artifacts(cmd,
         for filename in os.listdir(os.path.join(input_path, 'artifacts')):
             artifact_name = filename.split('.')[0]
             filepath = os.path.join(input_path, 'artifacts', filename)
-            with open(filepath) as artifact_file:
-                try:
-                    artifact = json.load(artifact_file)
-                    art_dict[artifact_name] = artifact
-                except json.decoder.JSONDecodeError as ex:
-                    raise CLIError('JSON decode error for {}: {}'.format(filepath, str(ex))) from ex
+            # skip hidden files
+            if ((os.name != 'nt' and not filename.startswith('.')) or
+                    (os.name == 'nt' and not bool(os.stat(filepath).st_file_attributes & stat.FILE_ATTRIBUTE_HIDDEN))):
+                with open(filepath) as artifact_file:
+                    try:
+                        artifact = json.load(artifact_file)
+                        art_dict[artifact_name] = artifact
+                    except json.decoder.JSONDecodeError as ex:
+                        raise CLIError('JSON decode error for {}: {}'.format(filepath, str(ex))) from ex
     except FileNotFoundError as ex:
         raise CLIError('File not Found: {}'.format(str(ex))) from ex