UBUNTU: [Packaging] Bind hv_vss_daemon startup to hv_vss device

BugLink: https://bugs.launchpad.net/bugs/1891224

Update the systemd service for the vss daemon and add a new udev rule
to ensure the service will not fail in case vss is not enabled for the
guest.

The udev rules is responsible for starting the service only when the
vss device is available. In the unit file, the service is now bound to
the device unit, so the service can be stopped if the device is
removed. And the service is also conditioned to the existence of the
device, this way we avoid starting and stopping the service during
boot if the device is not available.
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

debian/linux-cloud-tools-common.hv-vss-daemon.service

@@ -4,6 +4,8 @@
 [Unit]
 Description=Hyper-V VSS Protocol Daemon
 ConditionVirtualization=microsoft
+ConditionPathExists=/dev/vmbus/hv_vss
+BindsTo=sys-devices-virtual-misc-vmbus\x21hv_vss.device
 
 [Service]
 ExecStart=/usr/sbin/hv_vss_daemon -n

debian/linux-cloud-tools-common.hv-vss-daemon.udev

+SUBSYSTEM=="misc", KERNEL=="vmbus/hv_vss", TAG+="systemd", ENV{SYSTEMD_WANTS}+="hv-vss-daemon.service"

debian/rules.d/3-binary-indep.mk

@@ -200,6 +200,7 @@ ifeq ($(do_tools_hyperv),true)
 	dh_installinit -p$(cloudpkg) -n --name hv-vss-daemon
 	dh_installinit -p$(cloudpkg) -n --name hv-fcopy-daemon
 	dh_installudev -p$(cloudpkg) -n --name hv-kvp-daemon
+	dh_installudev -p$(cloudpkg) -n --name hv-vss-daemon
 	dh_systemd_enable -p$(cloudpkg)
 	dh_installinit -p$(cloudpkg) -o --name hv-kvp-daemon
 	dh_installinit -p$(cloudpkg) -o --name hv-vss-daemon