InMemory Ticketer
To test out external ticketing plugin integration, Inmemory ticketer plugin is added as a OSGi feature.
This can be installed by adding feature opennms-inmemory-ticketer.
Once installed, use opennms:inmemory-ticketer karaf command to query/update ticket state.
| Configurations has to be made in the Horizon etc directory.
      We reference etcrelative to the OpenNMS Horizon Core home directory.
      Depending on your operating system the home directory is/usr/share/opennmsfor Debian/Ubuntu or/opt/opennmsfor CentOS/RHEL. | 
Create a OpenNMS properties file to enable the ticketer plugin
sudo vi etc/opennms.properties.d/inmemory-ticketer.propertiesSet OSGi based ticketer plugin and enable it
opennms.ticketer.plugin = org.opennms.netmgt.ticketd.OSGiBasedTicketerPlugin
opennms.alarmTroubleTicketEnabled = true