JBoss ON agent fails to start due to a required plug-in missing from the dependency graph

Issue

• The RHQ agent (rhq-agent) is not starting cleanly.
• Agent fails to start and logs the following error:

        FATAL [main] (org.rhq.enterprise.agent.AgentMain)- {AgentMain.start-failure}Failed to start the agent
        java.lang.RuntimeException: Cannot initialize the plugin container
            at org.rhq.core.pc.plugin.PluginManager.initialize(PluginManager.java:176)
            at org.rhq.core.pc.PluginContainer.startContainerService(PluginContainer.java:488)
            at org.rhq.core.pc.PluginContainer.initialize(PluginContainer.java:306)
            at org.rhq.enterprise.agent.AgentMain.startPluginContainer(AgentMain.java:1926)
            at org.rhq.enterprise.agent.AgentMain.start(AgentMain.java:660)
            at org.rhq.enterprise.agent.AgentMain.main(AgentMain.java:429)
        Caused by: java.lang.IllegalArgumentException: Plugin [JMX] is required by plugins [[Hibernate]] but it does not exist in the dependency graph yet
            at org.rhq.core.clientapi.agent.metadata.PluginDependencyGraph.getDeepDependencies(PluginDependencyGraph.java:329)
            at org.rhq.core.clientapi.agent.metadata.PluginDependencyGraph.getDeepDependencies(PluginDependencyGraph.java:342)
            at org.rhq.core.clientapi.agent.metadata.PluginDependencyGraph.getDeploymentOrder(PluginDependencyGraph.java:245)
            at org.rhq.core.pc.plugin.PluginManager.initialize(PluginManager.java:155)
            ... 5 more

• Agent's plug-in container can not be initialized when a dependent plug-in is not installed.