Fix install of pip and sbt plugin for asdf

What does this MR do?

Fix some issues with installation scripts

• pip for python 2.7 now needs a specific install script
• sbt plugin for asdf is temporary broken and we need a local fix untill upstream is fixed.

This MR fixes the failing jobs of the build stage only. This won't fix existing failures of the test stage related to the current broken master issue.

What are the relevant issue numbers?

gitlab-org/gitlab#298720 (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
  • Job definition example
  • CI Templates (to be removed)
  • Vendored CI Templates (also in CE)
  • Ensure that all of the ENV vars supported are propagated to Docker containers upon docker run in job definitions
• Conforms to the code review guidelines
• Security reports checked/validated by reviewer