Try out a new nova.conf.sample format

The current format strikes me as fairly bizarre:

  - Having the help message after the option it's documenting seems
    backwards to me. Compare to the glance or swift samples.

  - Printing the type as e.g. "(StrOpt)" isn't very user friendly

  - We're creating a global pound symbol shortage

Switch to a new format that looks much more like a normal config file.

Change-Id: Ifba0a181667f3b81cad400f1cdd3812e388a9d64
Merge "Try out a new nova.conf.sample format"