ClusterExternalizableUtil ignores provided ClassLoader instances

[guusdk]

The ClusterExternalizableUtil class is the strategy implementation for the ExternalizableUtil class.

This class has various methods that read data. The method accepts a Classloader instance to be provided, from which the data is read. The current implementation ignores the provided class loader, and instead uses either the Hazelcast-plugin classloader, or the context class loader from the thread that is invoking the method.

Note that this issue is very similar to https://igniterealtime.atlassian.net/browse/OF-2350, which describes the same issue in the DefaultExternalizableUtil class.