Re: How to restore to previous state after automatic update
That's good. You have the system running again.
You'll probably have the exact same problem the next time you (or someone else) updates plugins. This is a good time to switch to Java 8, and confirm that you have successfully switched to Java 8.
You'll need to install Java 8 on the machine, confirm that Java 8 is the default Java, then find the Jenkins configuration which starts your Jenkins server, confirm it is using Java 8, then verify Java 8 is used from the "System Information" page for the master agent.