Add capability to download file from s3 (#826)

* add capability to download file from s3

* fix flake8 error

Author: cmadjar

python/lib/aws_s3.py

@@ -77,3 +77,22 @@ def check_if_file_key_exists_in_bucket(self, file_key):
             return False
 
         return True
+
+    def download_file(self, s3_object_name, destination_file):
+        """
+        Download a file from an S3 bucket
+
+        :param s3_object_name: S3 object name to download from
+         :type s3_object_name: str
+        :param destination_file: Full path where the file should be downloaded
+         :type destination_file: str
+        """
+
+        s3_prefix = f"s3://{self.bucket_name}/"
+        s3_file_name = s3_object_name[len(s3_prefix):] if s3_object_name.startswith(s3_prefix) else s3_object_name
+
+        try:
+            print(f"Downloading {s3_file_name} from {self.aws_endpoint_url}/{self.bucket_name} to {destination_file}")
+            self.s3_bucket_obj.download_file(s3_file_name, destination_file)
+        except ClientError as err:
+            raise Exception(f"{s3_object_name} download failure = {format(err)}")