The JDK7 job brought CI to an standstill and Jenkins had to be restarted.

It's unclear whether this is due to JDK7 itself, or due to the 68MB+ log that the job generates:
https://infinispan.ci.cloudbees.com/job/Infinispan-master-JDK7-tcp/18/console

The log should be reduced first, try running the testsuite and then enable the job in CI.