discovery-helper: reflect argument value in the name of the results It is common to create multiple pairs of repositories using different argument values. Recording the argument value in the results names has two main advantages: * It is easy to remember the value used to create a pair, * It get simpler to create multiple pair at the same time from the same source. Previously, running: `./discovery-helper.sh pypy 50 10` would create a `pypy-left` and `pypy-right` repository. Now it will create `pypy-50h-10d-left` and `pypy-50h-10d-right`.

discovery-helper: echo the stripped revsets early Having them printed early make it easy for a user to just grab the generated revset and directly uses them