fix(XoBackups#deltaCopyVm): do not always delete base (#599)
fix(XoBackups#deltaCopyVm): do not always delete base (#599)

Only when there are no VMs with the TAG_SOURCE_VM for this source VM.
vatesfr/xo-web,lmcro/xo-web,lmcro/xo-web,lmcro/xo-web,vatesfr/xo-web