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
windows:
  - AD users can be pulled in via LDAP