Description of problem:
If a user runs the following call, they will receive the following traceback:

[root@oldceremony i386]# subscription-manager-cli register --username=<username> --password=<password>
1a918422-32f2-4914-9da7-4fb91526f2eb admin <username>
Traceback (most recent call last):
  File "/usr/sbin/subscription-manager-cli", line 69, in <module>
    sys.exit(abs(main() or 0))
  File "/usr/sbin/subscription-manager-cli", line 60, in main
    return managercli.CLI().main()
  File "/usr/share/rhsm/managercli.py", line 345, in main
    cmd.main()
  File "/usr/share/rhsm/managercli.py", line 70, in main
    self._do_command()
  File "/usr/share/rhsm/managercli.py", line 126, in _do_command
    self.certlib.update()
  File "/usr/share/rhsm/certlib.py", line 42, in update
    return update.perform()
  File "/usr/share/rhsm/certlib.py", line 116, in perform
    expected = uep.getCertificateSerials()
  File "/usr/share/rhsm/certlib.py", line 205, in getCertificateSerials
    reply = reply['serials']
TypeError: list indices must be integers, not str

Version-Release number of selected component (if applicable):
git HEAD

How reproducible:
Always

Steps to Reproduce:
1. Install the latest subscription-manager
2. Run subscription-manager-cli register --username=<username> --password=<password>, replacing these with values appropriate for your chosen Candlepin environment
  
Actual results:
As above

Expected results:
Registration succeeds

Additional info: