An agent log record with numeric params could be unformattable on the master

[jglick]

Noticed in a support bundle an agent log (nodes/slave/…/jenkins.log) with

…	WARNING	h.r.RemoteInvocationHandler$Unexporter#reportStats: The 15 minute average rate is {0,number,0.0}±{1,number,0.0}/sec. At the 95% confidence level this is above 100.0/sec. If this message is repeated often in the logs then very seriously consider setting system property ''hudson.remoting.RemoteInvocationHandler.Unexporter.retainOrigin'' to ''false'' to trade debug diagnostics for reduced memory pressure.

This is from https://github.com/jenkinsci/remoting/blob/a09a8dd40e3269f578a503cee26b859e522ea6e2/src/main/java/hudson/remoting/RemoteInvocationHandler.java#L734-L745 but note the missing actual numbers (and '' where ' was meant). The reason is because of https://github.com/openjdk/jdk/blob/6bab0f539fba8fb441697846347597b4a0ade428/src/java.logging/share/classes/java/util/logging/LogRecord.java#L561-L565 plus https://github.com/openjdk/jdk/blob/6bab0f539fba8fb441697846347597b4a0ade428/src/java.logging/share/classes/java/util/logging/Formatter.java#L146-L148.

We could format every log record with parameters, which would be useful for code in the agent JVM doing something like

LOGGER.log(Level.INFO, "ran at {0} producing {1}", new Object[] {new Date(), someMutableObject});

but I went for the more conservative fix here.

Proposed changelog entries

• Ensure that log messages are not missing numeric parameters when log entries are created on an agent. In particular, fix logs collected by the Support Core plugin

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[oleg-nenashev]

Looks good, will proceed with merge taking other approvals.
Please create a Jira issue if you want to get it backported