Add ability to run a single test or a group

[rn]

With the original python based implementation one could run a single test or group of tests. Very useful when debugging and it would be nice if we could do:

rtf run foo.bar.baz

[dave-tucker]

You can as of 06358c6

[rn]

ah, then the help message needs updating:

# rtf run --help
A brief description of your command

Usage:
  rtf run [flags]

Flags:
  -h, --help   help for run

Global Flags:
  -c, --casedir string        Directory containing cases (default "cases")
  -e, --envVars stringSlice   Add a environment variable (multiple uses allowed)
  -x, --extra                 Add extra debug info to log files
  -l, --labels string         Labels to apply (comma separated)
      --logger string         <host>:<port> of a socket to log stdout to
  -r, --resultdir string      Directory to place results in (default "_results")
  -v, --verbose count[=-1]    Increase verbosity level

[dave-tucker]

ah so it does!

[dave-tucker]

Fixed in #17