snapcraft: Add missing snapcraft files from dist (make dist) archive

Signed-off-by: Martin Winter <mwinter@opensourcerouting.org>

snapcraft/Makefile.am

@@ -1,11 +1,5 @@
 EXTRA_DIST = snapcraft.yaml \
-   scripts/Makefile scripts/zebra-service scripts/bgpd-service \
-   scripts/isisd-service scripts/ripd-service scripts/ripngd-service \
-   scripts/ospf6d-service scripts/ospfd-service \
-   scripts/isisd-service scripts/pimd-service \
-   scripts/ldpd-service \
-   defaults/bgpd.conf.default defaults/isisd.conf.default \
-   defaults/ospf6d.conf.default defaults/ospfd.conf.default \
-   defaults/pimd.conf.default defaults/zebra.conf.default \
-   defaults/ripd.conf.default defaults/ripngd.conf.default \
-   defaults/ldpd.conf.default defaults/vtysh.conf.default
+   README.* \
+   scripts/Makefile scripts/*-service \
+   defaults/*.conf.default \
+   helpers setup