change_host_name.rb for TinyCore Linux

Most (at least boot2docker) TinyCore based vagrant boxes boot from memory and do no persist. I'm mentioning this, because if you were to restart a persistent tinycore box, /opt/bootsync.sh has its own `/usr/bin/sethostname box` statement, in which case we might need to make changes to the script I believe.

However, if the change_host_name method is run every time after the box is up (I'm new to vagrant, and I haven't tested this behaviour yet), this pull request LGTM.

(I'm trying landrush for docker containers, which uses hostname value from `config.vm.hostname`, setting which warns about missing change_host_name cap.)