Raise when creating a runner with invalid options, rather than when trying to execute it
We don't actually care about the options passed to spawn, just that they work
We have defaults to fall back to for this
Ensure full coverage of the process of building up a SIPp command in Runner
#prepare_command should not be part of Runner's public interface
Do less obvious string interpolation in preparing SIPp commands
Ensure that true is returned when a runner completes successfully
Reduce spec duplication in expectations on SIPp being executed
Remove an unnecessary return statement
Merge branch 'master' into feature/runner_specs

Conflicts:
	lib/sippy_cup/runner.rb
Merge pull request #29 from mojolingo/feature/runner_specs

Add specs for and cleanup Runner