repos: git: Strip of heads/ prefix when checking out branches

If a remote branch is referenced as refs/heads/<branch>, also drop the
heads/ from the local branch name to have a consistent naming.

This wasn't noticed so far because the primary use case of refs/ is
addressing symbolic refs in upstream, and the related test case
(test_refspec_absolute) was papering over another hidden kas issues
while using refs/heads/.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kas/repos.py

@@ -443,7 +443,9 @@ class GitRepo(RepoImpl):
     def checkout_cmd(self, desired_ref, is_branch):
         cmd = ['git', 'checkout', '-q', self.remove_ref_prefix(desired_ref)]
         if is_branch:
-            cmd.extend(['-B', self.remove_ref_prefix(self.refspec)])
+            branch = self.remove_ref_prefix(self.refspec)
+            branch = branch[branch.startswith('heads/') and len('heads/'):]
+            cmd.extend(['-B', branch])
         if get_context().force_checkout:
             cmd.append('--force')
         return cmd