Comment 0 for bug 1667266

There are some issues in "--block-device-mapping" options of "server create" commands.

1. ValueError is raised if input don't contain "=". Sometimes the whole "server create" command is very complex, it's difficult to find out root reason directly, like this:

(openstack) server create --image cirros-0.3.5-x86_64-disk --flavor m1.tiny --nic net-id=d73b6234-91ff-466e-8b5d-141aa9b48ac8 --block-device-mapping vdb0ac9844f-2122-47a4-9a1b-676c59cdd662 chenrui_vm
need more than 1 value to unpack
(openstack)

2. If input "vdb=", not add any mapping information, the server will be launched successfully, not raise error message to let use add volume/snapshot id, just ignore "--block-device-mapping" option

(openstack) server create --image cirros-0.3.5-x86_64-disk --flavor m1.tiny --nic net-id=d73b6234-91ff-466e-8b5d-141aa9b48ac8 --block-device-mapping vdb= chenrui_vm
...

3. The help message of "block-device-mapping" option is so simple, need to add some details about how to add <type>, <delete_on_terminate> contains.

  --block-device-mapping <dev-name=mapping>
                        Map block devices; map is
                        <id>:<type>:<size(GB)>:<delete_on_terminate> (optional
                        extension)