Fix bad error message if you use an unknown CLI option.

This causes the check's constructor to fail, and thus subsequently calling check.critical fails
as the constructor never returned a check object, this results in a second exception, meaning
that the error message about the check is never shown to the user.

Rather than calling check.cricial, we now do what it does manually, so that we'll always print the
unexpected exception that we caught.
Remove Gemfile.lock
Fix fail with bundler due to overriding environment variables. Fixes
tests on ruby 1.8.7
Do not prepend Sensu::Plugin::CLI to the output error
Merge pull request #60 from bobtfish/fix_badcli_options_errormessage

Fix bad error message if you use an unknown CLI option.