Update API document with BootDevice

This patch adds description about above BootDevice Web APIs.
* GET v1/nodes/(node_uuid)/management/boot_device
* GET v1/nodes/(node_uuid)/management/boot_device/supported
* PUT v1/nodes/(node_uuid)/management/boot_device

Change-Id: I2826e59332102b258b72e9850baa1a6b0d189f79
Merge "Update API document with BootDevice"