Add optional parameter to set JJB version from PIP

Allow set version constraint when installing JJB using PIP, like

parameters:
  jenkins:
    job_builder:
      source:
        engine: git
        version: '>=1.6.0,<2.0.0'
...

i.e. version string is just added to the package name:

  jenkins-job-builder>=1.6.0,<2.0.0

Change-Id: I5e295ab25a19dd61a3fa40b36a69f75d2d0053f9
1 file changed