Make 04_catalog test reproducible

We start by inserting a row corresponding to one of the existing database,
excluding any database named "test".  But we later insert a fake record for a
database with oid 1, which is also the oid of an existing database.  So also
exclude this database oid from the list of existing database to make sure it
doesn't cause any problem (which actually happens with postgres 9.5 for some
reason).

expected/04_catalog.out

@@ -25,6 +25,7 @@ INSERT INTO "PoWA".powa_catalog_database_src_tmp
     FROM "PoWA".powa_catalog_database_src(0) src
     WHERE src.datname != current_database()
     AND src.datname != 'test'
+    AND src.oid != 1
     LIMIT 1;
 SELECT "PoWA".powa_catalog_database_snapshot(1);
  powa_catalog_database_snapshot 

sql/04_catalog.sql

@@ -15,6 +15,7 @@ INSERT INTO "PoWA".powa_catalog_database_src_tmp
     FROM "PoWA".powa_catalog_database_src(0) src
     WHERE src.datname != current_database()
     AND src.datname != 'test'
+    AND src.oid != 1
     LIMIT 1;
 SELECT "PoWA".powa_catalog_database_snapshot(1);