[fuel-devops][feature]Add autocomplete for commands

[Rodion Promyshlennikov]

Add feature to make able autocomplete for dos.py sub-commands.
For example:
dos.py <tab keypress>
     list Show virtual environments
    show Show VMs in environment
    erase Delete environment
    start Start VMs
    destroy Destroy(stop) VMs
    suspend Suspend VMs
    resume Resume VMs
    revert Apply snapshot to environment
    snapshot Make environment snapshot
    sync Synchronization environment and devops
    snapshot-list Show snapshots in environment
    snapshot-delete Delete snapshot from environment
    net-list Show networks in environment
    time-sync Sync time on all env nodes
    revert-resume Revert, resume, sync time on VMs
    version Show devops version
    create Create a new environment
    slave-add Add a node
    slave-change Change node VCPU and memory config
    slave-remove Remove node from environment
    admin-setup Setup admin node
    admin-change Change admin node VCPU and memory config
    node-start Start node in environment
    node-destroy Destroy (power off) node in environment
    node-reset Reset (restart) node in environment

dos.py revert-resume <tab keypress>
     <envname1>
     <envname2>
     ...
     <envnameN>

dos.py revert-resume <envname1> <tab keypress>
     <snapshot1>
     <snapshot2>
     ...
     <snapshotN>

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/310292

[OpenStack Infra (hudson-openstack)]

Change abandoned by Andreas Jaeger (<email address hidden>) on branch: master
Review: https://review.opendev.org/310292
Reason: This repo is retired now, no further work will get merged.