[JENKINS-27035] Gathering command read/write events (#3071)

* Slave.JnlpJar.getURL did not work in some modes when core had a snapshot dependency on Remoting.

* Starting to implement Channel.Listener.read/write.

* Now obtaining response timing statistics.

* For now, avoiding timestamped snapshots, as it caused problems for #3120 which I have asked for help from @stephenc diagnosing.

* Simplified logging a bit.

* onResponse

* hudson.FilePath$Mkdirs is a lot more readable than hudson.FilePath$13.

* Specific snapshot.

* onJar

* LoggingChannelListener

* remoting.version=3.17

* Making a few test assertions more lenient to adapt to https://github.com/jenkinsci/remoting/pull/247.