Run a script on VM's first boot

For administrators only maybe, it could be nice to customize VM's configuration on boot.

This can be done via a cloud-init script / user-data: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux_OpenStack_Platform/4/html/End_User_Guide/user-data.html

These configurations could also be stored as templates in the app database, for reuse' purposes. 
