fix callback_handler test resetting global Lua system & user paths
fix callback_handler test resetting global Lua system & user paths

Even though the config is specific to the client instance, inside the
Aerospike C client library the Lua system & user paths settings are
actually global setting. So initializing a new Client instance without
setting up the correct paths, will reset the Lua paths for other client
instances as well; even for already existing instances.

aerospike/aerospike-client-nodejs,aerospike/aerospike-client-nodejs,aerospike/aerospike-client-nodejs,aerospike/aerospike-client-nodejs,aerospike/aerospike-client-nodejs