Bogus servers should not be killable (fixes #250)
* style guide corrections ('&&', not 'and'; don't use single-letter variable names)
* also fixed a thing where security groups enumeration would die if a bogus server existed that's bit me before
* reviewed other knife cluster commands and made them not tolerate bogosity either
Version bump to 4.8.3
Regenerate gemspec for version 4.8.3