leapp upgrade throws error "RepoError: Parsing primary.xml error: Start tag expected, '<' not found"

Issue

• One gets below traceback error while executing leapp upgrade:

Traceback (most recent call last):
  File "/usr/lib64/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/usr/lib64/python2.7/multiprocessing/process.py", line 114, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib/python2.7/site-packages/leapp/repository/actor_definition.py", line 74, in _do_run
    actor_instance.run(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/leapp/actors/__init__.py", line 289, in run
    self.process(*args)
  File "/usr/share/leapp-repository/repositories/system_upgrade/common/actors/rpmscanner/actor.py", line 20, in process
    rpmscanner.process()
  File "/usr/share/leapp-repository/repositories/system_upgrade/common/actors/rpmscanner/libraries/rpmscanner.py", line 110, in process
    pkg_repos = get_package_repository_data()
  File "/usr/share/leapp-repository/repositories/system_upgrade/common/actors/rpmscanner/libraries/rpmscanner.py", line 77, in get_package_repository_data
    return _get_package_repository_data_yum()
  File "/usr/share/leapp-repository/repositories/system_upgrade/common/actors/rpmscanner/libraries/rpmscanner.py", line 31, in _get_package_repository_data_yum
    for pkg in yum_base.doPackageLists().installed:
  File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 2981, in doPackageLists
    avail = self.pkgSack.returnNewestByNameArch(patterns=patterns,
  File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 1075, in <lambda>
    pkgSack = property(fget=lambda self: self._getSacks(),
  File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 778, in _getSacks
    self.repos.populateSack(which=repos)
  File "/usr/lib/python2.7/site-packages/yum/repos.py", line 393, in populateSack
    raise Errors.RepoError(e.args[0])
RepoError: Parsing primary.xml error: Start tag expected, '<' not found

• The Trackback error is also observed in yum update sometimes.