Description of problem:
pulp-admin tab completion doesn't support docker plugin

Version-Release number of selected component (if applicable):
>> rpm -qa | grep pulp-server
pulp-server-2.5.0-0.6.beta.el6.noarch

How reproducible:
always

Steps to Reproduce:
>> pulp-admin -u admin -p admin 
auth      bindings  --config  consumer  --debug   event     -h        --help    iso       orphan    puppet    repo      rpm       server    tasks  

There is no docker option, however
>> pulp-admin --map | grep docker
docker: manage docker images
    uploads: upload docker images into a repository
    sync: sync a docker repository from an upstream index
    publish: publish a docker repository
    export: export a docker repository

Expected results:
>> pulp-admin -u admin -p admin 
auth      bindings  --config  consumer  --debug   docker    event     -h        --help    iso       orphan    puppet    repo      rpm       server    tasks