Description of problem:
Harmless but unnecessary error messages are thrown to agent log during upgrade.

Version-Release number of selected component (if applicable):
jon3.1.0.RC2

How reproducible:
Always

Steps to Reproduce:
1.follow upgrade procedure and upgrade JON.3.0.1.GA + some agent plugins to JON.3.1.0 
2. check the agent.log
  
Actual results:
similar messages (depends on what agent plugins was installed) are thrown to agent.log 
2012-06-05 14:38:36,775 WARN  [RHQ Server Polling Thread] (org.rhq.enterprise.agent.PluginUpdate)- {PluginUpdate.plugin-not-on-server}The plugin [plugins/rhq-agent-plugin-4.2.0.JON.3.0.1.GA.jar] does not exist on the Server - renaming it to [rhq-agent-plugin-4.2.0.JON.3.0.1.GA.jar.REJECTED] so it will not get deployed by the Plugin Container.
2012-06-05 14:38:36,775 ERROR [RHQ Server Polling Thread] (org.rhq.enterprise.agent.PluginUpdate)- {PluginUpdate.plugin-rename-failed}Failed to rename illegitimate plugin [plugins/rhq-agent-plugin-4.2.0.JON.3.0.1.GA.jar] to [rhq-agent-plugin-4.2.0.JON.3.0.1.GA.jar.REJECTED]. 

Expected results:
This is expected scenario (the old plugins are not available in upgraded system) so the ERROR log level is not necessary.