Fix races in v3 cells extension tests

A global was used for a cell list and tests would update this global
and fail depending on order run, etc.

Yes, this is the same fix as commit bb2c3c5 except for the v3
extension. Yes, copied and pasted code is utterly evil. No, we
apparently will never learn.

Closes-Bug: #1235399
Change-Id: I3406d0440aed38cbf3a9bedf24420fb867876b08
Merge "Fix races in v3 cells extension tests"