Add _FATAL_EXCEPTION_FORMAT_ERRORS global.

Add a new global variable to control when exception format errors
are fatal. The Glance functional/unit test now make use of this
to ensure exceptions are correctly formatted when testing.

Change-Id: I720336e10345a0e33937c7241c37f548d6f87ea2
Sample config and doc for the show_image_direct_url option.

This patch adds a sample configuration option to the
glance-api.conf sample and it explains how to use the option.

Change-Id: I1cc82a2cae0bbfc650ab7294ff08740bb868e4ff
Merge "Add _FATAL_EXCEPTION_FORMAT_ERRORS global."
Merge "Sample config and doc for the show_image_direct_url option."