code: public void enableVM(String hostname) throws IllegalStateException {
          logger.debug("Enabling VM " + hostname);
          assignableVMs.enableVM(hostname);
      }
docs: Enable the VM with the specified host name. Hosts start in an enabled state, so you only need to call
  this method if you have previously explicitly disabled the host.
  
  @param hostname the name of the host to enable
  @throws IllegalStateException if the scheduler is shutdown via the {@link #isShutdown} method.