Upgrading a version of Xubuntu (16.x to 17.x)

Well I had hoped to keep my mediapc running 16.04 with Qgis 313ec55 but it tells me I should update to a new version so I have followed the procedure to update to 16.10 and then 17.04. Unfortunately it automatically uninstalled Qgis as part of this and can’t reinstall from the Xenial repository for 16.10 so I have let it go off this machine. I have decided that mediapc may as well go to artful like the other computers as this is fairly stable. It is being updated quite a lot, there were a lot of new packages for the bedroom computer when I checked last night. 
Fortunately a virtual machine running 16.04 and 313ec55 on my mainpc has proved to be quite usable for nearly everything in Qgis and can be set to have two virtual displays making it relatively easy to keep editing maps on older versions of Qgis as will be necessary to continue with the project work and having the advantage of being on the mainpc which is the best ergonomically with the placement of screens in my desk layout.
I have had quite a few virtualbox VMs running all sorts of different Qgis versions because of various issues with different editions of the software but I can’t go back to 2.18 or earlier from 2.99 because of changes in the project format which would see a lot of stuff that would have to be put into the 2.18 project that would be a lot of work I would rather not have to do.
However because of some issues in this combination I still need a VM running 2.18 to run the composers for outputting pages of maps so that one will be used as well. The project version issues don’t affect the composers so it continues to work quite well.