Specify pipenv requirements explicitly

What does this MR do?

This MR changes the analyzer Dockerfile to makes pipenv's requirements explicit during installation. What this does is fix the issue of drifting version numbers in the expectations of our test projects.

The root cause of this issue comes from unspecified versions in the dependency list of pipenv. This MR takes the dependency list from the pip freeze of a current install of pipenv==2018.11.26.

Note: this MR removes the PIPENV_VERSION build arg from the Dockerfile and explicitly puts this into pipenv.requirements.txt file. The reasoning here is that if a user wants to rebuild the analyzer with a new pipenv version they can do so by tweaking the requirements file rather than the arg.

What are the relevant issue numbers?

gitlab-org/gitlab#207925 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer