core: Reintroduce `name` attribute for the `Guest`

Maintain compatibility for vagrant-vbguest plugin which uses it.
vagrant-vbguest doesn't use the caps system (to keep compatibility with
older Vagrant versions), but includes similar functionality itself.
core: Tweak host/guest capability logging

- Use downcase logger name as everywhere else
- Remove duplicate logging from the Guest
Merge pull request #2794 from tmatilai/cabability_host_name

core: reintroduce `name` attribute for the `Guest`
core: tests for Guest#name