Vagrant always looks at host memory for RAM building
Originally created by @anonym on #7166 (Redmine)
When the Vagrant builder VM is up, our Rakefile checks if enough memory for RAM building is available on the host, which effectively means “can we start another Vagrant VM”. In other words, the current check only makes sense when the VM is off.
When the VM is up we should instead look if the running VM has enough free memory.
Feature Branch: bugfix/7166-vagrant-memory-checks