Override dh_install-arch instead of dh_install

Closes: #806064

debian/control

@@ -5,7 +5,7 @@ Maintainer: Debian Libvirt Maintainers <pkg-libvirt-maintainers@lists.alioth.deb
 Uploaders: Guido Günther <agx@sigxcpu.org>, Laurent Léonard <laurent@open-minds.org>
 Testsuite: autopkgtest
 Build-Depends:
- debhelper (>= 7),
+ debhelper (>= 8.9.7~),
  dh-autoreconf,
  dh-systemd (>= 1.18~),
  dh-apparmor [linux-any],

debian/rules

@@ -145,7 +145,7 @@ override_dh_auto_test:
 	    exit 1; \
 	fi
 
-override_dh_install:
+override_dh_install-arch:
 	dh_install
 
 	# Don't ship virt-admin yet