Authentication could be required when performing REST API authenticated
queries over http(s) (done by run_http_exc). Typically, it appends with
gerrit behind apache2.
This change queries git credential for gerrit password when http request
returns a 401.
Change-Id: Iad60eea938c42210ba8c5df4a1b76f8d2f4dd76d
910ffddd1b