Fix maven.nuxeo.org instances monitoring

https://maven-us.nuxeo.org/nexus/ was not responding around 2019-07-15 18:30 (Paris)

Fixed with a simple restart since it looked like a Java process freeze according to the logs.

2019-07-15 16:09:13 INFO  [22250493-155051] - org.apache.http.impl.execchain.RetryExec - I/O exception (org.apache.http.NoHttpResponseException) caught when processing request to {s}->https://mavenin.nuxeo.com:443: The target server failed to respond
2019-07-15 17:17:59 INFO  [jetty-main-1   ] - org.sonatype.nexus.events.EventSubscriberHost - Initialized

sudo docker restart nexus2 

No alert has been sent => fix monitoring and alert

• consider healthcheck url
• consider Tomcat integration with Datadog or any other more relevant

Apply the same for maven-eu and, if relevant, do the same for all other Nexus instances or create dedicated tickets.

We don't know what went wrong and made Nexus unresponsive. The host server was still fine despite a high load.

https://app.datadoghq.com/dash/host/1132327781?live=undefinedh&tile_size=m