avoid bash_completion.sh appearing as an area for crowbar CLI

bash_completion.sh should not appear in the following usage:

```
cloud4-admin:~ # crowbar
Usage: crowbar <area> <subcommand>
  Areas: ceilometer ceph cinder crowbar database deployer dns glance heat ipmi keystone logging machines network neutron nfs_client node_state node_status nova nova_dashboard ntp pacemaker provisioner rabbitmq reset_nodes reset_proposal suse_manager_client swift trove updater watch_status
```