added subcommand servers to list servers

[berendt]

Example output of this subcommand:

$ vagrant rackspace servers
==> devstack: Server Name          State                IPv4 address
==> devstack: devstack             ACTIVE               166.78.18.8

[berendt]

Any news here?

[krames]

@berendt Sorry about the delay. There has been some ongoing discussion in the Rackspace office about whether this functionality should be added to vagrant-rackspace or if this information should be accessed using the upcoming Unified OpenStack CLI.

I was hoping to delay this and refer you to that cli, but it seems like progress has been slower than expected. For reason, I am going to go ahead and accept these after I get a chance to review them.

Again...sorry about the delay and thanks for the contribution!

[krames]

@berendt Can I get you to update the custom commands section to include you newly added commands?

Other than that, it looks great! Thanks again!

[krames]

This PR is ready to go. Once the documentation is completed in PR #94 I will merge this in.