Add driver-properties command

Add 'driver-properties <driver_name>' command. This returns a table
listing the properties of the specified driver, including name
and description.

Eg:
$ ironic driver-properties pxe_ipmitool
+--------------------+----------------------------------------------+
| Property           | Description                                  |
+--------------------+----------------------------------------------+
| ipmi_address       | IP address or hostname of the node. Required.|
| ipmi_password      | password. Optional.                          |
| ipmi_priv_level    | privilege level; default is ... Optional.    |
| ipmi_terminal_port | node's UDP port ... required for console...  |
| ipmi_username      | username; default is NULL user. Optional.    |
| pxe_deploy_kernel  | UUID (from Glance) of the deployment...      |
| pxe_deploy_ramdisk | UUID (from Glance) of the ramdisk...         |
+--------------------+----------------------------------------------+

If this feature is not available in Ironic, it returns
"Not Found (HTTP 404)".

If driver_name doesn't exist, it returns "The driver '<driver-name>' is
unknown. (HTTP 404)".

Change-Id: Id125fe4c1771dc5bb5b57d528940f2ba1c85866a
Blueprint: get-required-driver-info