Description of problem:
Before a consumer is registered, it gives a nice little warning about it:
warning: this client is not known to the pulp server; run 'pulp-consumer consumer register' to register it
But if a consumer is registered and then unregistered, a much more ambiguous error message pops up:
error:  operation failed: Invalid SSL Certificate

How reproducible:
Always

Steps to Reproduce:
1. register consumer
2. unregister consumer (via pulp-admin on server)
3. try any command
  
Actual results:
error:  operation failed: Invalid SSL Certificate

Expected results:
warning: this client is not known to the pulp server; run 'pulp-consumer consumer register' to register it