Jenkins Pipeline compatibility

[erik-am]

GitVersion includes support for Jenkins as a build system, but this only supports traditional Jenkins jobs, not the new way of using Jenkins Pipeline.

Currently, you can find all kinds of workarounds on the web to make GitVersion play nicely with Jenkins Pipeline-as-code. This pull request aims to fix it within GitVersion so that one doesn't need workarounds in his pipeline.

Current problems:

• GitVersion expects the branch name in the environment variable GIT_BRANCH while using Jenkins. This is true for the old Git plugin, but when using Jenkins pipeline, the branch name is stored in BRANCH_NAME instead.
  A workaround that people use is to add env.GIT_BRANCH = env.BRANCH_NAME in the Jenkinsfile, but this pollutes the pipeline.
• Somehow Jenkins will add two remotes origin and origin1 when executing the Pipeline.
  GitTools will therefore fail with the error "2 remote(s) have been detected"
  A workaround to remove the duplicate origin has been posted at http://stackoverflow.com/questions/39475135/gitversion-in-a-jenkins-multibranch-pipeline-job
• Within a pull request, both the pull request number and the number of commit should be taken into account, e.g., 1.0.4-PullRequest0005.3. However, the actual result was 1.0.4-PullRequest.3, missing the PR number and therefore leading to duplicates. This can be fixed by changing the default tag number pattern from [/-](?<number>\d+)[/-] to [/-](?<number>\d+).

[erik-am]

The build and tests pass in AppVeyor, but fail in Travis CI.
I see that's the case for other PR's as well, so I guess that's normal?

[JakeGinnivan]

Nice work

[JakeGinnivan]

And yeah, travis is stuffed...