One trick you can employ is to send restart signal and save rest of the provisioning work as a script to be run on boot:
config.vm.provision "shell", inline: <<-SHELL
echo "Do your thing... DONE"
cat <<-RCLOCAL | sed -s 's_^ __' > /etc/rc.local
#!/bin/bash
echo "This will be run once on next boot and then it's destroyed and never run again"
rm /etc/rc.local
RCLOCAL
chmod o+x /etc/rc.local
shutdown -r now #restart
SHELL
This was tested to work on debian 9, so you may need to enable services or find another way to get your code bootsrapped to run on the next boot if you're running something else.
Unfortunately you can't simply do:
config.vm.provision "shell", inline: "shutdown -r now"
config.vm.provision "shell", inline: "echo 'hello world'"
results in ==>
The SSH connection was unexpectedly closed by the remote end. This
usually indicates that SSH within the guest machine was unable to
properly start up. Please boot the VM in GUI mode to check whether
it is booting properly.