Return proper error if no test dir found

[etheroji]

No description provided.

[sabhiram]

From the build log:

  1) EthPM integration successfully installs and provisions a package with dependencies from EthPM:
     Error: Timeout of 15000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves.

Given that it passes the test in the other instance, might just be a timeout issue.