MetadataNotifier keep one active DB connection

[fxp]

While settings the maxIdle parameter to 0 in the pool configuration, user can find a permanent IDLE in transaction connection to the DB.

Looking at the relation used in the DB, we can notice that one connection is always used by the MetadataNotifier due to openDirect call:

dbms = (Dbms) srvContext.getResourceManager().openDirect(Geonet.Res.MAIN_DB);

which pass the dbms to the metadata notifier threads and keep it until GeoNetwork stops (MetadataNotifierControl shutdown).

We could probably only open a db connection while the MetadataNotifierTask looks for changes to notify.

[fxp]

Committed revision 8578.