TT#66582 Ensure proper/old version of prosody is installed

We had to downgrade prosody in mr7.5 and have to check it is
still old/pinned version in use until we are ready for the upgrade.
See workfront ticket 66583 for more details here.

Change-Id: I7cad16c1d08beb57d52eca5f83fbcc1d21dba7c9

templates/310_package-ngcp.yaml.tt2

@@ -84,3 +84,8 @@ package:
 
   odbc-mariadb:
     installed: true
+
+  prosody:
+    installed: true
+    versions:
+    - 0.9.12-2+deb9u2+bpo10+1