Refactor acloud.public.errors to acloud.errors.

Bug: 113753798
Test: atest acloud_test && run acloud create/list/delete
Change-Id: I03b4b34769d754bfebd279895b0ca44311bbecc7
diff --git a/internal/lib/auth.py b/internal/lib/auth.py
index 966e72e..819abc8 100644
--- a/internal/lib/auth.py
+++ b/internal/lib/auth.py
@@ -47,7 +47,7 @@
 from oauth2client.contrib import multistore_file
 from oauth2client import tools as oauth2_tools
 
-from acloud.public import errors
+from acloud import errors
 
 logger = logging.getLogger(__name__)
 HOME_FOLDER = os.path.expanduser("~")