"No vagrantfile" error catched as "unknow error"

[julienvey]

when running a custom command in a folder with no Vagrantfile

> vagrant openstack image-list
An unknow error happened in Vagrant OpenStack provider

To easily debug what happened, we recommend to set the environment
variable VAGRANT_OPENSTACK_LOG to debug

    $ export VAGRANT_OPENSTACK_LOG=debug

If doing this does not help fixing your issue, there may be a bug
in the provider. Please submit an issue on Github at
https://github.com/ggiamarchi/vagrant-openstack-provider
with the stracktrace and the logs.

We are looking for feedback, so feel free to ask questions or
describe features you would like to see in this provider.
A Vagrant environment or target machine is required to run this
command. Run `vagrant init` to create a new Vagrant environment. Or,
get an ID of a target machine from `vagrant global-status` to run
this command on. A final option is to change to a directory with a
Vagrantfile and to try again.

But should only be

> vagrant openstack image-list
A Vagrant environment or target machine is required to run this
command. Run `vagrant init` to create a new Vagrant environment. Or,
get an ID of a target machine from `vagrant global-status` to run
this command on. A final option is to change to a directory with a
Vagrantfile and to try again.