Enable security in packaging tests (elastic/x-pack-elasticsearch#4216)

Now that security is not enabled by default for a trial license, the
packaging tests are failing because they expect security to be
enabled. This commit adds enabling security in all instances started
during the packaging tests.

Original commit: elastic/x-pack-elasticsearch@9838393ecb

qa/vagrant/src/test/resources/packaging/utils/xpack.bash

@@ -94,6 +94,7 @@ generate_trial_license() {
     sudo -E -u $ESPLUGIN_COMMAND_USER sh <<"NODE_SETTINGS"
 cat >> $ESCONFIG/elasticsearch.yml <<- EOF
 xpack.license.self_generated.type: trial
+xpack.security.enabled: true
 EOF
 NODE_SETTINGS
 }