TT#44917 Ship certain modules only on Debian/stretch

The prosody version in Debian/buster already provides module,
we're trying to ship here.

Therefore failing to install e.g. with:

| trying to overwrite '/usr/lib/prosody/modules/mod_mam/fallback_archive.lib.lua', which is also in package prosody 0.10.2-1

Install the conflicting modules only on Debian 9, AKA stretch.

Change-Id: I4535b8c2963f40d5b2093922e6050404855b5004

debian/control

@@ -6,6 +6,7 @@ Homepage: https://www.sipwise.com/
 Standards-Version: 3.9.8
 Build-Depends:
  debhelper (>= 10~),
+ lsb-release,
  quilt,
 
 Package: ngcp-prosody-modules

debian/rules

@@ -15,6 +15,17 @@ override_dh_auto_configure:
 override_dh_install:
 	dh_install
 	find debian/ngcp-prosody-modules/ -name README.\* -delete
+	# conflicts with prosody >=0.10.2-1 in Debian/buster
+	if lsb_release -rs | grep -q '^9' ; then \
+		echo "Keeping all modules for Debian stretch"; \
+	else \
+		echo "Removing conflicting modules (shipped by prosody in Debian)"; \
+		find debian/ngcp-prosody-modules/ -name fallback_archive.lib.lua -delete; \
+		find debian/ngcp-prosody-modules/ -name mamprefs.lib.lua -delete; \
+		find debian/ngcp-prosody-modules/ -name mamprefsxml.lib.lua -delete; \
+		find debian/ngcp-prosody-modules/ -name mod_mam.lua -delete; \
+		find debian/ngcp-prosody-modules/ -name mod_websocket.lua -delete; \
+	fi
 
 override_dh_auto_clean:
 	rm -f debian/README_mod_*.*