Reformat output text of pav show *_config

[tygoetsch]

The formatting for the output of pav show test_config is cramped and misleading. It leads the reader to identify the description of the command below the one they are searching for as being for the command they are searching for.

example:

# SLURM(): description
slurm:
# AVAIL_STATES(): description
#    more description
avail_states: []
# UP_STATES(): description
#    more description
up_states: []

Maybe provide more traditional help formatting as well as example usages (separate examples for if you are setting the variable in a config file or passing on the command-line.