cgit_atom_feed: Better exception handling

In case of HTTP error on requesting cgit atom feed, you will see an
exception like this:

```
python38/root/usr/lib64/python3.8/urllib/request.py", line 649, in http_error_default
    raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 404: Not found
```

This is not good for troubleshooting.

This PR changes to use `requests` and `tenacity` library to handle HTTP
requests and retries. You will see the following exception in case of
HTTP error:

```
Traceback (most recent call last):
  File "/Users/yux/Library/Python/3.10/lib/python/site-packages/tenacity/__init__.py", line 407, in __call__
    result = fn(*args, **kwargs)
  File "/Volumes/Workspaces/projects/openshift/doozer/./doozerlib/metadata.py", line 319, in _make_request
    resp.raise_for_status()
  File "/Users/yux/Library/Python/3.10/lib/python/site-packages/requests/models.py", line 941, in raise_for_status
    raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 404 Client Error: Not found for url: https://pkgs.devel.redhat.com/cgit/rpms/openshift-clients/atom/?h=rhaos-4.8-rhel-7

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/Volumes/Workspaces/projects/openshift/doozer/./doozerlib/runtime.py", line 101, in wrapper
    return func(*args, **kwargs)
  File "/Volumes/Workspaces/projects/openshift/doozer/./doozerlib/runtime.py", line 113, in wrapper
    return func(*args)
  File "/Volumes/Workspaces/projects/openshift/doozer/./doozerlib/runtime.py", line 1584, in <lambda>
    lambda meta, _: (meta, meta.needs_rebuild()),
  File "/Volumes/Workspaces/projects/openshift/doozer/./doozerlib/metadata.py", line 624, in needs_rebuild
    hint = self._target_needs_rebuild(el_target=target)
  File "/Volumes/Workspaces/projects/openshift/doozer/./doozerlib/metadata.py", line 663, in _target_needs_rebuild
    atom_entries = self.cgit_atom_feed(commit_hash=distgit_commitish, branch=self.branch())
  File "/Volumes/Workspaces/projects/openshift/doozer/./doozerlib/metadata.py", line 322, in cgit_atom_feed
    content = retry(
  File "/Users/yux/Library/Python/3.10/lib/python/site-packages/tenacity/__init__.py", line 324, in wrapped_f
    return self(f, *args, **kw)
  File "/Users/yux/Library/Python/3.10/lib/python/site-packages/tenacity/__init__.py", line 404, in __call__
    do = self.iter(retry_state=retry_state)
  File "/Users/yux/Library/Python/3.10/lib/python/site-packages/tenacity/__init__.py", line 361, in iter
    raise retry_exc from fut.exception()
tenacity.RetryError: RetryError[<Future at 0x11160beb0 state=finished raised HTTPError>]
```

doozerlib/metadata.py

@@ -1,30 +1,31 @@
-from typing import Dict, Optional, List, Tuple, Any, Union
-import urllib.parse
-import yaml
-from collections import OrderedDict
-import pathlib
-import io
 import datetime
-import time
-import sys
+import io
+import pathlib
 import re
+import sys
+import time
+import urllib.parse
+from collections import OrderedDict
 from enum import Enum
-
+from typing import Any, Dict, List, NamedTuple, Optional, Tuple, Union
 from xml.etree import ElementTree
-from typing import NamedTuple
-import dateutil.parser
 
+import dateutil.parser
+import requests
+import yaml
 from dockerfile_parse import DockerfileParser
-import doozerlib
+from tenacity import (retry, retry_if_exception_type, stop_after_attempt,
+                      wait_fixed)
 
-from doozerlib.pushd import Dir
-from doozerlib.distgit import ImageDistGitRepo, RPMDistGitRepo
+import doozerlib
 from doozerlib import exectools, logutil
+from doozerlib.assembly import assembly_basis_event, assembly_metadata_config
 from doozerlib.brew import BuildStates
-from doozerlib.util import isolate_el_version_in_brew_tag, isolate_git_commit_in_release
-
-from doozerlib.model import Model, Missing
-from doozerlib.assembly import assembly_metadata_config, assembly_basis_event
+from doozerlib.distgit import ImageDistGitRepo, RPMDistGitRepo
+from doozerlib.model import Missing, Model
+from doozerlib.pushd import Dir
+from doozerlib.util import (isolate_el_version_in_brew_tag,
+                            isolate_git_commit_in_release)
 
 
 class CgitAtomFeedEntry(NamedTuple):
@@ -311,14 +312,19 @@ def cgit_atom_feed(self, commit_hash: Optional[str] = None, branch: Optional[str
                 branch = self.branch()
             if not commit_hash and branch:
                 params["h"] = branch
-        if params:
-            url += "?" + urllib.parse.urlencode(params)
 
-        req = exectools.retry(
-            3, lambda: urllib.request.urlopen(url),
-            check_f=lambda req: req.code == 200)
+        def _make_request():
+            self.logger.info("Getting cgit atom feed %s ...", url)
+            resp = requests.get(url, params=params)
+            resp.raise_for_status()
+            return resp.text
+
+        content = retry(
+            stop=stop_after_attempt(3),  # wait for 10 seconds * 3 = 30 seconds
+            wait=wait_fixed(10),  # wait for 10 seconds between retries
+            retry=retry_if_exception_type(),
+        )(_make_request)()
 
-        content = req.read()
         et = ElementTree.fromstring(content)
 
         entry_list = list()