use dh_installsystemd for guest agent (#916625)

debian/control-in

@@ -442,6 +442,7 @@ Package: qemu-guest-agent
 Architecture: any
 Multi-Arch: foreign
 Depends: ${shlibs:Depends}, ${misc:Depends}, lsb-base (>= 3.0-6)
+Pre-Depends: ${misc:Pre-Depends}
 Description: Guest-side qemu-system agent
  QEMU is a fast processor emulator: currently the package supports
  ARM, CRIS, i386, M68k (ColdFire), MicroBlaze, MIPS, PowerPC, SH4,

debian/rules

@@ -257,6 +257,7 @@ ifeq (${enable_system},enable)
 		debian/qemu-system-common/etc/qemu-ifup
 endif
 	dh_installinit -a -pqemu-guest-agent
+	dh_installsystemd -a -pqemu-guest-agent --no-start --no-enable
 	dh_link -a
 	dh_lintian -a
 	dh_strip -a