Fix the following network command documentation issues:
- Fix format of subnet pool positional arguments
- Update port set options to match help
- Fix network command documentation for Network v2
versus Compute v2 options and commands
- Fix subnet command documentation errors and formatting
problems in help text
Change-Id: I808c2a70ca62eafc9e42d6873539cdd142ffe50c
Related-Bug: #1558677