Convert the p4 binary error into a warning for the dev server.
Review Request #8623 — Created Jan. 16, 2017 and submitted — Latest diff uploaded
We fail to start the dev server if a user has p4python installed but the p4 binary is not in the path. This converts it into a warning, and adds instructions for downloading p4.
Tested with and without p4 installed. Saw the warning only when it wasn't
installed. The dev server continued to work.