Add support for OpenBMC

[luke-jarymowycz]

Must include:
power functions
user credential operations

[joelrebel]

@zevweiss does the OpenBMC we're shipping expose redfish endpoints? atleast it seemed like it based on some of your work here https://github.com/bmc-toolbox/bmclib/pull/167/files

[zevweiss]

Yeah, it's got both redfish and ipmi available, though there may be gaps in their respective implementations regarding certain operations -- I'm pretty sure power control should be available via both, but I've never tested user/password management operations.