The registration process via the Subscription Manager command encounters an error: "pkg_resources.DistributionNotFound: six."

Issue

• When executing subscription-manager commands, an error traceback is observed:

  # subscription-manager refresh
  Traceback (most recent call last):
  File "/sbin/subscription-manager", line 5, in <module>
  from pkg_resources import load_entry_point
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 3007, in <module>
  working_set.require(__requires__)
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 728, in require
  needed = self.resolve(parse_requirements(requirements))
  File "/usr/lib/python2.7/site-packages/pkg_resources.py", line 626, in resolve
  raise DistributionNotFound(req)   
  pkg_resources.DistributionNotFound: six