8284: Fix Jolokia discovery issues

[skarsaune]

This fixes two bugs with Jolokia discovery:

1. serious : repeated discovery runs crash. Runing repeatedly in the background is the whole point
2. more of an annoyance: the PR disables JMC agent by omitting JVM info in the descriptor (as presence is interpreted as a local JVM)
   Both tested OK.

---

Progress

• Commit message must refer to an issue
• Change must be properly reviewed (1 review required, with at least 1 Committer)

Issue

• JMC-8284: Fix Jolokia discovery issues (Bug - P2)

Reviewing

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$ git fetch https://git.openjdk.org/jmc.git pull/597/head:pull/597
$ git checkout pull/597

Update a local copy of the PR:
$ git checkout pull/597
$ git pull https://git.openjdk.org/jmc.git pull/597/head

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$ git pr checkout 597

View PR using the GUI difftool:
$ git pr show -t 597

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[bridgekeeper]

👋 Welcome back skarsaune! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[skarsaune]

@aptmac : Are you able to create a bug for this. Or two if that is preferrable.
Details on the bugs:

SEVERE: Cannot register MBean jolokia:type=Discovery,agent=jmc: javax.management.InstanceAlreadyExistsException: jolokia:type=Discovery,agent=jmc
javax.management.InstanceAlreadyExistsException: jolokia:type=Discovery,agent=jmc
	at java.management/com.sun.jmx.mbeanserver.Repository.addMBean(Repository.java:322)
	at java.management/com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerWithRepository(DefaultMBeanServerInterceptor.java:1848)
	at java.management/com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerDynamicMBean(DefaultMBeanServerInterceptor.java:945)
	at java.management/com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerObject(DefaultMBeanServerInterceptor.java:880)
	at java.management/com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerMBean(DefaultMBeanServerInterceptor.java:315)
	at java.management/com.sun.jmx.mbeanserver.JmxMBeanServer.registerMBean(JmxMBeanServer.java:523)
	at org.jolokia.server.core.service.impl.MBeanRegistry.registerMBeanAtServer(MBeanRegistry.java:80)
	at org.jolokia.server.core.service.impl.MBeanRegistry.registerMBean(MBeanRegistry.java:54)
	at org.jolokia.server.core.service.impl.JolokiaServiceManagerImpl.registerMBean(JolokiaServiceManagerImpl.java:409)
	at org.jolokia.server.core.service.impl.JolokiaContextImpl.registerMBean(JolokiaContextImpl.java:45)
	at org.jolokia.server.core.service.api.AbstractJolokiaService.registerJolokiaMBean(AbstractJolokiaService.java:98)
	at org.jolokia.service.discovery.JolokiaDiscovery.init(JolokiaDiscovery.java:45)
	at org.openjdk.jmc.jolokia.JolokiaDiscoveryListener.discoverJvms(JolokiaDiscoveryListener.java:70)
	at org.openjdk.jmc.jolokia.AbstractCachedDescriptorProvider$Scanner.scan(AbstractCachedDescriptorProvider.java:86)
	at org.openjdk.jmc.jolokia.AbstractCachedDescriptorProvider$Scanner.run(AbstractCachedDescriptorProvider.java:70)
	at java.base/java.lang.Thread.run(Thread.java:1583)

2. This option does not make sense for Jolokia:

[aptmac]

@skarsaune I've rolled both of these issues into one ticket if that's okay, I think it fits with this PR that accomplishes both at once.

https://bugs.openjdk.org/browse/JMC-8284

[skarsaune]

Ensure that only one instance is instantiated (linked to the lifecycle of this plugin). If one tries to instantiate another, it will attempt to register an MBean and sinply crash

[mlbridge]

Webrevs

• 01: Full - Incremental (21515ce8)
• 00: Full (b29d9841)

[aptmac]

There's a fix to the spotbugs config that will fix the Mac tests just an fyi

[skarsaune]

There's a fix to the spotbugs config that will fix the Mac tests just an fyi

Indeed, the test passed after merging in master 😄