ZenJMX config cycle creates duplicate call objects unnecessarily

[chris]

Every 6 hours ZenJMX issues a config call to get a list of data sources of type JMX. It then creates call objects based on the configuration.

To avoid creating duplicates we keep a cache of hashcodes associated with previous calls. If the hashcode has already been seen we don't create a new call.

There's a problem in the hashcode calculation that has resulted in duplicate calls being created.

[chris]

(In [7451]) refs #1886, #2309: discard the hashcode from the Map representation of
the datasource config. this is a different value each time and
results in duplicated call objects.