Add sample config files for commands

This commit adds a sample config file for each of the current 3
commands in subunit2sql. The files contain the current list of options
which can potentially be set in  a config file when using the command.
However for some of the arguments it doesn't make any sense to use them
outside of the cli.

The sample config files can be generated using the oslo-config-generator
utility with the config files added in the config-generator dir.

Change-Id: Ie578f99f27553e14fca4153a9ac5b5aa1c7eb49e
Merge "Add sample config files for commands"