Fix DumpRenderTree2 to serve HTTP tests on http://127.0.0.1:8000

Currently DumpRenderTree2 serves HTTP tests on http://localhost:8080.
Some of the tests hardcode 'http://127.0.0.1:8000' for resources, so
we must use this scheme and port for the requests to be same-origin.

This fixes LayoutTest http/tests/appcache/credential-url.html

Change-Id: I2a9c402fc7b0e0b62eb4a278d67ac0e63ef96e8b