Add dry run for command line

[PrzemekWirkus]

Cloned from: https://linaro.atlassian.net/browse/WPERF-825

We use wperf test to test some of the WindowsPerf internals. But we do not have decent CLI parse + dry run + exit.

Linux perf has:

       --dry-run
           Parse options then exit. --dry-run can be used to detect
           errors in cmdline options.

We can add --dry-run command line option to user_request class to emit after parsing parsed output and exit. This option should support also JSON output support.

Definition of done

• Add new command line option -dry-run.
• For user_request command line option parser, if --dry-run is specified, after parsing all CLI options we should output:
  • To stdout (as normal text) all command line options values already parsed.
    • these can be in parsable by Python strings e.g. if used specify -c 0,1,2 (and --json) we can print:

--json            : True
-c                : [0, 1, 2]

• We can do not have to cover all the command line options first. We can start with few most important ones like: -c, -e, -m, -n, --output, ( --timeout, sleep ) and -i, bool flags like --json, -t and -q.
• Add JSON output support - please note that you should use PrettyTable to do the output.