util: script to get DNS Shotgun pipeline results

util: script to get DNS Shotgun pipeline results

The shotgun performance tests are executed in a different repository, in
a couple of different pipelines. To hide away the complexity, this
script takes the pipeline ID of the triggered pipeline and then takes
care of the rest - waits for the pipeline to finish, locates the child
pipeline and the relevant results. The output from this script is a
convenient link to the charts with the results once they're available.

GitLab also has a mechanism which can wait for another pipeline.
However, it can't be utilized here, since there are variables which
need to be passed in when the pipeline is triggered (like protocol to be
tested, load, runtime etc.). This isn't currently supported by the
GitLab feature.