Fixed problem making variable to Null for memory clean

Author: mmornati

src/main/java/hudson/plugins/libvirt/Hypervisor.java

@@ -171,7 +171,6 @@ public synchronized Map<String, Domain> getDomains() throws LibvirtException {
  LogRecord rec = new LogRecord(Level.INFO, "Closing hypervisor connection");
  LOGGER.log(rec);
  hypervisorConnection.close();
- hypervisorConnection = null;
  } else {
  LogRecord rec = new LogRecord(Level.SEVERE, "Cannot connect to datacenter {0} as {1}/******");
  rec.setParameters(new Object[]{hypervisorHost, username});