Avoid full repo with all the history gets cloned about jenkins-library

[marcusholl]

The issue was opened during a discussion with a colleague about heavy projects in terms of repository size as some kind of a reminder.

After having a closer look into this issue:
normally piper lib does not clone by itself. Clone is done by corresponding SCM plugins. Should be solved on that level. Jenkins git SCM plugin is able to do shallow clones. See "Additional Behaviours" -> "Advanced clone behaviours". There we can specify the depth and/or a refspec.

There are also disadvantages or situation where is will not work that nice: e.g. performing merge commits between a branch head and the (potential) target of the merge are hard to do on a shallow copy. The change management related steps requires also all commits between origin/master and a (PR) branch head since we scan the commit messages for the change document id.

[marcusholl]