Merge pull request #13 from jaymzh/logging

Support telling chef-zero to log.
chef-zero exception handling

Role upload failure case was not covered
Merge pull request #15 from odcinek/retry_role_upload_failure

chef-zero exception handling
Make custom user work as expected
Fix for ssh processes not getting killed
Use group ids for both cases
Lint
Merge pull request #16 from odcinek/fix_custom_user

Make custom user work as expected
Clear the ref number when restarting

Currently if you do a 'taste-tester restart', then next test/upload
will fail.
Merge pull request #17 from jaymzh/fixrestart

Clear the ref number when restarting
Minor chef-zero logging fix

Don't do stupid string interpolation.
Don't delete files that don't exist.