core-image-ptest: Define a fallback for SUMMARY field

core-image-ptest: Define a fallback for SUMMARY field

Fixes errors like below seen with bitbake core-image-ptest-fast

WARNING: core-image-ptest-apr-util-1.0-r0 do_recipe_qa: QA Issue: Recipe core-image-ptest-apr-util in /mnt/b/yoe/master/sources/poky/meta/recipes-core/images/core-image-ptest.bb does not contain a SUMMARY. Please a
dd an entry. [missing-metadata]

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 307381c9267eb3a3e687c577a0afd552d44248f7)
Signed-off-by: Steve Sakoman <steve@sakoman.com>