Add get/set boot mode to Management Interface

Today, Ironic has a capability to boot a node in either BIOS/UEFI boot mode.
This blueprint is to introduce two new functions get_boot_mode, set_boot_mode
to management Interface to get the current boot mode and to set the boot mode
for the next boot respectively. Different drivers can implement this interface.
A command line interface will be created for the above functions.

Currently, IPMI doesn't support the above functionality. This blueprint will
add the support in iLO drivers.