classes/testimage-auto: add class to allow automatically running image tests

Setting TEST_IMAGE = "1" alone will now automatically run tests on the
image immediately after the image is built instead of having to add
INHERIT += "testimage" and run bitbake -c testimage <image> manually
(but that will still work). This restores functionality that was
present in the older imagetest-qemu class with IMAGETEST.

(From OE-Core rev: 72269a8fbec35c39af30fbabb1fa9ca7c5ee8d69)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/testimage-auto.bbclass

@@ -0,0 +1,23 @@
+# Copyright (C) 2013 Intel Corporation
+#
+# Released under the MIT license (see COPYING.MIT)
+
+
+# Run tests automatically on an image after the image is constructed
+# (as opposed to testimage.bbclass alone where tests must be called
+# manually using bitbake -c testimage <image>).
+#
+# NOTE: to use this class, simply set TEST_IMAGE = "1" - no need to
+# inherit it since that will be done in image.bbclass when this variable
+# has been set.
+#
+# See testimage.bbclass for the test implementation.
+
+inherit testimage
+
+python do_testimage_auto() {
+    testimage_main(d)
+}
+addtask testimage_auto before do_build after do_rootfs
+do_testimage_auto[depends] += "qemu-native:do_populate_sysroot"
+do_testimage_auto[depends] += "qemu-helper-native:do_populate_sysroot"