CHEF-4734: Stop enforcing group/owner regular expressions

for unix:
- user/group cannot start with '-', '+' or '~'
- user/group cannot contain ':', ',' or non-space-whitespace or null byte
- we already allowed spaces (i don't know why, but it was tested for)
- this fixes UTF-8 chars as well
CHEF-4734: tests for AD users on Unix hosts

- AD users can be pulled in via LDAP
- We already had tests for this in user+group specs
add utf-8 magic for ruby <= 1.9