use correct directory for install_virtualenv

[mcgibbon]

Purpose

This PR fixes the daint performance plan by using the correct directory for install_virtualenv.sh, since the duplicate copy under the fv3core directory has been deleted.

Checklist

Before submitting this PR, please make sure:

• [x] You have followed the coding standards guidelines established at Code Review Checklist.
• [x] Docstrings and type hints are added to new and updated routines, as appropriate
• [x] All relevant documentation has been updated or added (e.g. README, CONTRIBUTING docs)
• [x] For each public change and fix in pace-util, HISTORY has been updated
• [x] Unit tests are added or updated for non-stencil code changes

[mcgibbon]

Launched performance plan at https://jenkins.ginko.ch/job/pace-fv3core-performance-test/605/

[mcgibbon]

one GPU savepoint test timed out, will force merge