dpkg: Correct paths in postinst

The postinstall needs to reference $D, not ${D} which would get expanded
by bitbake. This allows postinsts to run correctly on the target system.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
build-appliance: Update to latest dylan revision for release

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>