fix: add exponential backoff

[PertsevRoman]

trafficstars

I faced with DNS/timeout issues during agent initialization WebSocket mode

io.jenkins.remoting.shaded.javax.websocket.DeploymentException: Connection failed.
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.container.jdk.client.JdkClientContainer$1.call(JdkClientContainer.java:187)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.container.jdk.client.JdkClientContainer$1.call(JdkClientContainer.java:107)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.container.jdk.client.JdkClientContainer.openClientSocket(JdkClientContainer.java:192)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.client.ClientManager$3$1.run(ClientManager.java:647)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.client.ClientManager$3.run(ClientManager.java:696)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.client.ClientManager$SameThreadExecutorService.execute(ClientManager.java:849)
	at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:112)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.client.ClientManager.connectToServer(ClientManager.java:493)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.client.ClientManager.connectToServer(ClientManager.java:337)
	at hudson.remoting.Engine.runWebSocket(Engine.java:656)
	at hudson.remoting.Engine.run(Engine.java:495)
Caused by: java.nio.channels.UnresolvedAddressException
	at sun.nio.ch.Net.checkAddress(Net.java:104)
	at sun.nio.ch.UnixAsynchronousSocketChannelImpl.implConnect(UnixAsynchronousSocketChannelImpl.java:302)
	at sun.nio.ch.AsynchronousSocketChannelImpl.connect(AsynchronousSocketChannelImpl.java:210)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.container.jdk.client.TransportFilter.handleConnect(TransportFilter.java:184)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.container.jdk.client.Filter.connect(Filter.java:80)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.container.jdk.client.Filter.connect(Filter.java:83)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.container.jdk.client.Filter.connect(Filter.java:83)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.container.jdk.client.ClientFilter.connect(ClientFilter.java:99)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.container.jdk.client.JdkClientContainer.connectSynchronously(JdkClientContainer.java:326)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.container.jdk.client.JdkClientContainer.access$700(JdkClientContainer.java:58)
	at io.jenkins.remoting.shaded.org.glassfish.tyrus.container.jdk.client.JdkClientContainer$1.call(JdkClientContainer.java:156)
	... 12 more

TCP socket mode

java.io.IOException: Failed to connect to http://jenkins-url/tcpSlaveAgentListener/: connect timed out
	at org.jenkinsci.remoting.engine.JnlpAgentEndpointResolver.resolve(JnlpAgentEndpointResolver.java:214)
	at hudson.remoting.Engine.innerRun(Engine.java:733)
	at hudson.remoting.Engine.run(Engine.java:539)
Caused by: java.net.SocketTimeoutException: connect timed out
	at java.net.PlainSocketImpl.socketConnect(Native Method)
	at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
	at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
	at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
	at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
	at java.net.Socket.connect(Socket.java:607)
	at sun.net.NetworkClient.doConnect(NetworkClient.java:175)
	at sun.net.www.http.HttpClient.openServer(HttpClient.java:463)
	at sun.net.www.http.HttpClient.openServer(HttpClient.java:558)
	at sun.net.www.http.HttpClient.<init>(HttpClient.java:242)
	at sun.net.www.http.HttpClient.New(HttpClient.java:339)
	at sun.net.www.http.HttpClient.New(HttpClient.java:357)
	at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1228)
	at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1162)
	at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1056)
	at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:990)
	at org.jenkinsci.remoting.engine.JnlpAgentEndpointResolver.resolve(JnlpAgentEndpointResolver.java:211)
	... 2 more

I'm trying to detect exact issue. Seems it relates to some K8s/JDK networking corner case. Anyway the PR introduces exponential backoff workaround which resolves the issue on source code level. It can help to avoid potential network issues.

[jglick]

Merge conflict, possibly with #603 etc. The idea is fine but this is probably a candidate for closing unless the author still has time and interest in cleaning it up.