buildserver: run_via_vagrant_ssh() to run cmds via python-vagrant
buildserver: run_via_vagrant_ssh() to run cmds via python-vagrant

This moves the last vagrant call in a subprocess.

f-droid/fdroid-server,fdroidtravis/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver,f-droid/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver,f-droid/fdroid-server,fdroidtravis/fdroidserver,f-droid/fdroidserver,f-droid/fdroid-server,fdroidtravis/fdroidserver,f-droid/fdroidserver