Refactor to new rspec format

Signed-off-by: Karl Isenberg <kisenberg@pivotal.io>
Validate Openstack CPI options with membrane

Signed-off-by: Karl Isenberg <kisenberg@pivotal.io>
Change OpenStack use_config_drive to config_drive

config_drive now specifies the device type that is
configured in OpenStack with config_drive_cdrom option.
It can be either cdrom or disk.

If it is not specified OpenStack servers created without
config drive.

Signed-off-by: Karl Isenberg <kisenberg@pivotal.io>
Normalize OpenStack CPI options

Remove keys with nil values

Signed-off-by: Karl Isenberg <kisenberg@pivotal.io>
Consider config drive when picking device for persistent disk

When OpenStack is using config drive as disk it will occupy one
of the devices. CPI takes this into account when choosing the
device name for persistent disk.

Signed-off-by: Karl Isenberg <kisenberg@pivotal.io>