Forking daemon after initializing hypervisor connection can cause
problems (and actually does in case of libvirt).
To notify systemd when daemon is ready use notify socket (previously it
was termination of parent process).
Not only refresh the info about mounted devices, but also check for
others - detected before xenstored was running. Because of recent change
in udev rules (adding flock) it shouldn't deadlock now.
It is common for both dom0 and VM, and also quite linux-specific
(other OSes will need other implementation). So move to linux-specific
repo (not dom0-specific).
