print reasonable error message when something wron with repo

fixing
Traceback (most recent call last):
  File "/usr/bin/spacewalk-repo-sync", line 100, in <module>
    sys.exit(abs(main() or 0))
  File "/usr/bin/spacewalk-repo-sync", line 93, in main
    sync.sync()
  File "/usr/lib/python2.6/site-packages/spacewalk/satellite_tools/reposync.py",
line 100, in sync
    self.import_packages(plugin, repo_id, url)
  File "/usr/lib/python2.6/site-packages/spacewalk/satellite_tools/reposync.py",
line 303, in import_packages
    packages = plug.list_packages(filters)
  File "/usr/lib/python2.6/site-packages/spacewalk/satellite_tools/repo_plugins/
yum_dnf_src.py", line 151, in list_packages
    self.sack.populate(self.repo, 'metadata', None, 0)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 164, in populate
    if self._check_db_version(repo, mydbtype):
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 222, in _check_db
_version
    return repo._check_db_version(mdtype)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1263, in _check_d
b_version
    repoXML = self.repoXML
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1462, in <lambda>
    repoXML = property(fget=lambda self: self._getRepoXML(),
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1458, in _getRepo
XML
    raise Errors.RepoError, msg

yum.Errors.RepoError: Cannot retrieve repository metadata (repomd.xml) for
repository: centos6-x86_64. Please verify its path and try again

backend/satellite_tools/repo_plugins/yum_dnf_src.py

@@ -141,7 +141,11 @@ def setup_repo(self, repo):
 
         warnings = YumWarnings()
         warnings.disable()
-        repo.baseurlSetup()
+        try:
+            repo.baseurlSetup()
+        except:
+            warnings.restore()
+            raise
         warnings.restore()
         repo.setup(False)
         self.sack = self.repo.getPackageSack()