Add Kraken to known_host

[12/27/18 11:09:31] [SSH] Opening SSH connection to 51.254.197.210:32799.
Key exchange was not finished, connection is closed.
java.io.IOException: There was a problem while connecting to 51.254.197.210:32799
	at com.trilead.ssh2.Connection.connect(Connection.java:834)
	at hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:1324)
	at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:831)
	at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:820)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
Caused by: java.io.IOException: Key exchange was not finished, connection is closed.
	at com.trilead.ssh2.transport.KexManager.getOrWaitForConnectionInfo(KexManager.java:95)
	at com.trilead.ssh2.transport.TransportManager.getConnectionInfo(TransportManager.java:237)
	at com.trilead.ssh2.Connection.connect(Connection.java:786)
	... 7 more
Caused by: java.io.IOException: The server hostkey was not accepted by the verifier callback
	at com.trilead.ssh2.transport.KexManager.handleMessage(KexManager.java:548)
	at com.trilead.ssh2.transport.TransportManager.receiveLoop(TransportManager.java:790)
	at com.trilead.ssh2.transport.TransportManager$1.run(TransportManager.java:502)
	... 1 more
[12/27/18 11:09:31] Launch failed - cleaning up connection
[12/27/18 11:09:31] [SSH] Connection closed.