Stop obfuscating errors in configuration test

[confluence]

There are multiple places in the configuration test where specific errors are hidden or conflated. This test should expose errors which are as specific as possible to the user, since its purpose is to debug configuration problems.

One example:

• the test is reporting: ✖ Error: Cannot execute kill script (error status 2. Please check your killCommand option
• there is no information available on what that error status actually means -- the script is probably relaying it from the kill command, and status 2 is usually used for "misuse of shell built-ins".
• there should be an error message also available in the child process object, but we don't print or log it, so this information is inaccessible.