build: Add testing config option

build: Add testing config option

This patch comes from below commit of upstream
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commit df43b3dad829e8b7f79fd15c20d997f50e745ae7
Author: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Date:   Wed Jan 4 15:24:45 2017 +0200

    build: Add testing config option

    This adds --enable-testing that can be used to enable emulator and tester
    which are no longer experimental but also are not meant for production.
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Change-Id: I41edb9f1b726340dde4a22bc705a68b5bceea4c9
Signed-off-by: Anupam Roy <anupam.r@samsung.com>