retag-images: fix YAML module errors

- Don't use yaml.FullLoader class. It's unsafe and doesn't exist in
  older versions of PyYAML

- Fix code that tried to parse Docker REST JSON output using PyYAML. Use
  the json module instead.

TESTS
=======================================
Run "retag-images.sh --dryrun" with both tags that already exist and
tags that don't exist in DockerHub, and make sure there are no Python
exceptions; in the following environments:

* CentOS 7 / python 2.7.5
  - pyyaml 3.10  (centos)
  - pyyaml 5.4.1 (pypi.org)

* Ubuntu 18 / python 2.7.17
  - pyyaml 3.12  (ubuntu)
  - pyyaml 5.4.1 (pypi.org)

Closes-Bug: 1981107
Signed-off-by: Davlet Panech <davlet.panech@windriver.com>
Change-Id: I9a7ecfd51ffb955f3ccc8f9b26ef610740fa400b

build-tools/build-docker-images/tag-management/retag-images.sh

@@ -51,7 +51,7 @@ import yaml
 
 for fname in sys.argv[1:]:
     with open(fname) as f:
-        imgs = yaml.load_all(f, Loader=yaml.FullLoader)
+        imgs = yaml.safe_load_all(f)
         for entry in imgs:
             for img in entry.get("images"):
                 print ("%s|%s|%s|%s" % (
@@ -108,8 +108,8 @@ function retag_and_push_image {
         else
             curl -k -sSL -X GET https://${docker_registry}/v2/${image}/tags/list \
                 | python -c '
-import sys, yaml, json, re
-y=yaml.load(sys.stdin.read(), Loader=yaml.FullLoader)
+import sys, json, re
+y=json.loads(sys.stdin.read())
 RC=1
 if y and sys.argv[1] in [img for img in y.get("tags")]:
     RC=0