Fix argument for configdrive usage
Fix argument for configdrive usage

The argument name defined must match how it is used in the code. Fix
--config-drive to be --configdrive, to match the code. Fix the metavar
as well while we're here, though it only has an effect on help, docs,
etc.

This wasn't caught by tests because shell arguments are mocked there,
and the gate doesn't use the CLI at all.

Change-Id: Iac1bf91388b79deee971088a53dd86167ca3fb29
Closes-Bug: #1419940

openstack/python-ironicclient,openstack/python-ironicclient,NaohiroTamura/python-ironicclient,bcrochet/python-ironicclient,NaohiroTamura/python-ironicclient,rdo-management/python-ironicclient