test/config: add replicaset failure testing helper

The module now has only one function, which allows to reduce a
boilerplace code needed to verify a scenario, when all instances of a
replicaset should fail with the same error message.

The module will be extended with replicaset management functions later.

NO_DOC=testing helper
NO_CHANGELOG=see NO_DOC
NO_TEST=see NO_DOC