Fix cp command for artifacts to exclude the directory holding the artifacts.
Fix cp command for artifacts to exclude the directory holding the artifacts.

Summary:
There are currently paths that look like "artifacts/artifacts/coverage.xml" because
the cp command includes the src directory, not just its contents.

Test Plan: Tested that path.join("a", "b", ".") results in "a/b" rather than "a/b/c"

Reviewers: nate, kylec

Reviewed By: nate, kylec

Subscribers: changesbot, anupc

Differential Revision: https://tails.corp.dropbox.com/D155680

dropbox/changes-client,dropbox/changes-client