Do not use deprecated destroyConfigBean in config tests

Replace org.opendaylight.controller.config.util.ConfigTransactionJMXClient
destroyConfigBean with destroyModule in tests.
Test resource leaks in FixedThreadPoolConfigBeanTest.

Change-Id: If3847d3cb9211d9e830006400c258dad9e6ffb35
Signed-off-by: Tomas Olvecky <tolvecky@cisco.com>
Merge "Do not use deprecated destroyConfigBean in config tests"