New options for `obmcutil`

Hello,

I've got a patch-series that reworks obmcutil to remove some cruft, use some more standard python techniques and also to add some new commandline options that make it more effective (at least, in my opinion).

The series does remove some truly esoteric capabilities, but I expect those who care (if anyone) can do the job in other ways (e.g. busctl). All the 'normal' commands are retained, i.e:

* {power,chassis}{on,off}
* {bmc,chassis,host,}state
* bootprogress
* power

If you're keen to review it, the series is here:

https://gerrit.openbmc-project.xyz/#/q/project:openbmc/skeleton+branch:master+topic:obmcutil-rework

The essence of the series for end users is:

1. obmcutil will now block rather than die with an exception when invoked before necessary objects are available on DBus:

    https://gerrit.openbmc-project.xyz/7276

2. There is now a --wait option to make it block until a command is complete, and give an appropriate exit status:

    https://gerrit.openbmc-project.xyz/7257/

2. And there is a --verbose option, which largely exists to complement --wait, which will dump the journal to stdout until the command is complete:

    https://gerrit.openbmc-project.xyz/7258

If you're interested, please review!

Cheers,

Andrew