Should paths in args.path be added to the beginning of sys.path?

[qyearsley-zz]

Reason: If one puts paths to libraries in the beginning of sys.path when running tests, it ensures that the same version of that library is used by everyone who runs the test, regardless of whether they have a different version installed on their system.

For example: When running the perf dashboard tests, even though I specify paths to required libraries through args.path, for a couple of the libraries I also happen to have other versions installed on my system, and those are used instead.

Specific proposed change: In Host.add_to_path, call sys.path.insert(0, path(absolute_path) instead of sys.path.append(absolute_path).

[dpranke]

Yes, that seems reasonable.