Remove requirement for .packages for pub run test
Remove requirement for .packages for pub run test

This won't exist before you run getPackages, and because we cache the result (and can't easily invalidate it) it often gets out of date.

Fixes #2080.

Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code,Dart-Code/Dart-Code