Remove non-needed "boolean" options arguments
Pass the whole config hash to Knife::Bootstrap
Add `--solo` option to bootstrap with knife-solo

Support `--[no-]solo` command line option as well as `knife[:solo]`
configuration option. Show the option always in the usage message,
but error with instructions if knife-solo gem is not found when solo
bootstrap method is chosen.
Update knife-solo instructions in the readme
Merge pull request #6 from tmatilai/knife-solo-integration

knife-solo integration