Tags to choose either agent or server install.
Use default package manager on the conditional. Yeah, might break but we can add specific package names on a distribution conditional if we get to that...
Switch from variables to defaults so they're always overridden.
Clearer message.  Cores are per CPU, and we install one agent  per Core, per CPU
Use a role, not tasks, so that it works with defaults and such in a predicatble manner.  See Vagrantfile on how this works with local testing.
Switched base boxes. Override Ansible roles path so Vagrant's provision just works. Removed the extra vars and using role defaults.  Dropped the private network -- it's not required and Vagrant 1.5.1 breaks Fedora.