Bug 1127411 - WARN [Thread-6] (rhq.core.pc.plugin.PluginClassLoader)- Failed to purge embedded jars directory. Cause: java.io.IOException

Destroy Plugin Class Loaders only once (IOException came from the
directory being already purged)

(cherry picked from commit 494e37ae3d140e250fb84ad0346c5159570eb6b0)