debian/rules: --no-start for xen dh_installinit

debian/rules: --no-start for xen dh_installinit

While debugging the xen-utils postinst/prerm to find the cause of the
mysteriously disappearing xenconsoled processes, I discovered that the
xen-utils-common postinst and prerm stop and start the xen init script
as well!

These commands are not visible in the packaging code, but they are added
by dh_installinit into the postinst and prerm during package build time.

We only want to call the script from xen-utils-V, so disable this
behavior by using --no-start

Signed-off-by: Hans van Kranenburg <hans@knorrie.org>
Reviewed-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
Closes: #932759 (2/2)