Improve error message if you forgot to make the base box

[rosiel]

If you don't remember that you don't have an islandora_base base box yet, and run vagrant up, then you get a very non-helpful error message:

mbp:islandora-playbook [git:dev+?] rlefaive$ vagrant up
Bringing machine 'default' up with 'virtualbox' provider...
==> default: Importing base box 'islandora_base'...
==> default: Matching MAC address for NAT networking...
==> default: Setting the name of the VM: Islandora 8 Ansible Sandbox Instance
The name of your virtual machine couldn't be set because VirtualBox
is reporting another VM with that name already exists. Most of the
time, this is because of an error with VirtualBox not cleaning up
properly. To fix this, verify that no VMs with that name do exist
(by opening the VirtualBox GUI). If they don't, then look at the
folder in the error message from VirtualBox below and remove it
if there isn't any information you need in there.

VirtualBox error:

VBoxManage: error: Could not rename the directory '/Users/rlefaive/VirtualBox VMs/Islandora 8 Ansible Base Box_1673546208745_46366' to '/Users/rlefaive/VirtualBox VMs/Islandora 8 Ansible Sandbox Instance' to save the settings file (VERR_ALREADY_EXISTS)
VBoxManage: error: Details: code NS_ERROR_FAILURE (0x80004005), component SessionMachine, interface IMachine, callee nsISupports
VBoxManage: error: Context: "SaveSettings()" at line 3649 of file VBoxManageModifyVM.cpp

The solution to this immediate problem is just to run again with ISLANDORA_BUILD_BASE=true. But surely we could abort early instead?