Updated iossim output path to use $(SYMROOT).

Previously it was hardcoded to use the xcodebuild folder.

BUG=NONE

Review URL: https://chromiumcodereview.appspot.com/14835006

git-svn-id: http://src.chromium.org/chrome/trunk/src/testing@198112 4ff67af0-8c30-449e-8e8b-ad334ec8d88c