Remove the HEAD check for a file being read in cloud storage

In addition to being unnecessary, it also causes read-after-write issues occasionally on S3

storage/cloud.py

@@ -114,9 +114,15 @@ class _CloudStorage(BaseStorageV2):
     self._initialize_cloud_conn()
     path = self._init_path(path)
     key = self._key_class(self._cloud_bucket, path)
-    if not key.exists():
-      raise IOError('No such key: \'{0}\''.format(path))
-    return key.get_contents_as_string()
+    try:
+      return key.get_contents_as_string()
+    except S3ResponseError as s3r:
+      # Raise an IOError in case the key was not found, to maintain the current
+      # interface.
+      if s3r.error_code == 'NoSuchKey':
+        raise IOError('No such key: \'{0}\''.format(path))
+
+      raise
 
   def put_content(self, path, content):
     self._initialize_cloud_conn()