Cannot detect error from init groovy script

You can get some error output like below:

```
/var/jenkins_home/init.groovy.d/initUsers.groovy: 1: unable to resolve class HudsonPrivateSecurityRealm
@ line 1, column 19.
def hudsonRealm = new HudsonPrivateSecurityRealm(false)
```

Our Jenkins replies on these groovy scripts. So, they must be successful.

Start by reproducing the error from /var/jenkins_home/init.groovy.d/initUsers.groovy and inspect how Jenkins reports failures from initialization scripts. The issue is complete when errors such as the unresolved HudsonPrivateSecurityRealm class are detected and the Jenkins initialization result is reliably reported.

Written by the indexing model from the issue text.