Replace System Rules with System Lambda

[stefanbirkner]

System Lambda is independent of the test framework while System Rules is
build for JUnit 4. We are using JUnit Jupiter and therefore System
Lambda is the better choice.

In addition System Lambda is more precise. It allows to set environment
variables for a single statement only. This already improves the
readability of the test because you can now immediately see which
environment variables are set when SystemInfo#findContainerDetails is
executed.

Checklist

• This is an enhancement of existing features, or a new feature in existing plugins
  • I have updated CHANGELOG.asciidoc
  • I have added tests that prove my fix is effective or that my feature works
  • Added an API method or config option? Document in which version this will be introduced
  • I have made corresponding changes to the documentation
• This is a bugfix
  • I have updated CHANGELOG.asciidoc
  • I have added tests that would fail without this fix
• This is a new plugin
  • I have updated CHANGELOG.asciidoc
  • My code follows the style guidelines of this project
  • I have made corresponding changes to the documentation
  • I have added tests that prove my fix is effective or that my feature works
  • New and existing unit tests pass locally with my changes
  • I have updated supported-technologies.asciidoc
  • Added an API method or config option? Document in which version this will be introduced
  • Added an instrumentation plugin? Describe how you made sure that old, non-supported versions are not instrumented by accident.
• This is something else
  • I have updated CHANGELOG.asciidoc

[cla-checker-service]

💚 CLA has been signed

[apmmachine]

💚 Build Succeeded

Expand to view the summary

Build stats

• Build Cause: [Started by user eyalkoren, Replayed #2]

• Start Time: 2020-10-11T05:59:42.369+0000

• Duration: 45 min 45 sec

Test stats 🧪

Test	Results
Failed	0
Passed	1610
Skipped	12
Total	1622

[eyalkoren]

@stefanbirkner Thanks!!
Please sign the CLA with your GitHub email, so that I can merge your changes.
Running tests in the mean time.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@2259495). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1434   +/-   ##
=========================================
  Coverage          ?   59.82%           
  Complexity        ?       91           
=========================================
  Files             ?      387           
  Lines             ?    17460           
  Branches          ?     2396           
=========================================
  Hits              ?    10445           
  Misses            ?     6299           
  Partials          ?      716           

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