Fix a minor nit with run-webkit-tests --android and the host port.

When running the android port, we need to create Port objects for
both the target (android) and host (linux). If you have an android
build in your checkout in src/out, then the linux port object tries
to figure out the architecture for the content_shell binary,
which is actually a directory and not a file at all. This patch
fixes that and we use the default architecture, which is good enough.

This gets rid of an annoying warning message at the start of
run-webkit-tests.

R=abarth@chromium.org, ojan@chromium.org, peter@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/23308005

git-svn-id: svn://svn.chromium.org/blink/trunk@156414 bbb929c8-8fbe-4397-9dbb-9b2b20218538