The tests in `DisconnectNodeCommandTest` are flaky. I noticed distinct test failure in CI during https://github.com/jenkinsci/jenkins/pull/10396.

Failed tests were,

• DisconnectNodeCommandTest#disconnectNodeManyShouldSucceed
• DisconnectNodeCommandTest#disconnectNodeShouldSucceedWithCause

the tests failed in different builds respectively, and ultimately both of them passed in another build.

Failure is always,

java.lang.AssertionError: 

Expected: an instance of hudson.slaves.OfflineCause$ByCLI
     but: <Connection was broken> is a hudson.slaves.OfflineCause$ChannelTermination 

Adopt the fix done for one of the tests in the same class by also asserting for 

https://github.com/jenkinsci/jenkins/pull/10307