HTTP check existing repositories

Instead of using git to check whether an existing opendev.org
repository exists when and upstream source is specified, just
use a simple HTTP check using urllib.

This avoids any authentication style guesses git clients may
make when a repo is not visible.

Change-Id: Ibee29eee84ae3890a9017edf287de1415d658c39

tools/check_valid_gerrit_projects.py

@@ -22,6 +22,8 @@ import re
 import shutil
 import sys
 import tempfile
+import urllib.error
+import urllib.request
 import yaml
 
 
@@ -221,8 +223,8 @@ def main():
             try:
                 # Check to see if we have already imported the project into
                 # OpenStack, if so skip checking upstream.
-                check_repo(openstack_repo, default_branch)
-            except git.exc.GitCommandError:
+                urllib.request.urlopen(openstack_repo)
+            except urllib.error.HTTPError:
                 # We haven't imported the repo yet, make sure upstream is
                 # valid.
                 found_errors += check_repo(upstream, default_branch)