Starting point for that refactoring: it turned out that the tests
was not independent. The DefaultValueCache which is a singleton
keeps the status over various tests. Success of test execution depends
on the order test execution.
We have now
* a dedicated rule for resetting the default value cache
* JenkinsConfiguration rule (which already provided facilities for
dealing with the configuration) has been replaced by a readYaml rule.
From the PipelineUnit test framework we get already a handler for
libraryResource, which is also part of the setup of the default
values.
* An auxiliar class which combines the
* JenkinsSetupRule (registers the lib)
* JenkinsReadYamlRule (provides facilities for Yaml parsing)
* JenkinsResetDefaultValueCacheRule (cleans up the DefaultValueCache)
into a rule chain. By using this rule chain we ensure that our
setup OK (piper lib registered, and default config can be setup in
a clean way).
