Because of Gradle's project lifecycle, disabling tasks in the script doesn't
work as expected, ./gradlew publish will still try to execute
:publishMavenJavaPublicationToMavenRepository and fail even if PUBLISH_ARTIFACTS
is set to false. To avoid that and make sure all publish tasks are disabled
script need to listen for tasks graph event to be ready and then disable the tasks.
with this change we're adding generation of 2 docker images - verifier and stub runner
we also added a project `spring-cloud-contract-stub-runner-boot` which contains a far jar with stub runner boot
fixes gh-526, gh-516
