Fetch full build list of job when incomplete

It's pull request #164 reworked with tests: automatically fetch missing builds metadata of a job when they are missing (Jenkins only returns metadata about the last 100 builds).

I have also added a `__str__` for `Plugins` because a `jenkins.get_plugins()` in the python console produces a `NotImplementedError`. And I have added some checks in the `jenkins_build.sh` script because it did not work out of the box in my environment.