Sorry, that is not written very well - it means localhost on the vagrant guest machine.
When you executed vagrant up, the last thing it output would have been its IP address - that is the address you should navigate to (this is the IP address of the virtual machine).
Now, in my virtual machine it appears this error: Fatal Error - sorry this shouldn't happen. SQLSTATE[28000] [1045] Access denied for user 'cms'@'172.17.0.4' (using password: YES)