Implicit jackson config (#1276)

* Replace static ObjectMappers with DockerClientConfig#getObjectMapper

* remove unused `ObjectMapper` field

* revert change

* simplify AbstrDockerCmdExec

* Remove unnecessary Jackson annotations

* Remove `anUnconfiguredCommandSerializesToEmptyJson` test case

* Try to disable the parallel test execution

* Add more logging, try just "hello"

* Revert the parallel change

* Back to sequential tests :(