[OE-core][PATCH 2/2] core-image-ptest.bb: use ?= for PTEST_EXPECT_FAILURE

[<Qi.Chen@windriver.com>]

From: Chen Qi <Qi.Chen@windriver.com>

We need to allow users to easily override this value in local.conf.
This has the benefit that 'bitbake core-image-ptest-xxx:do_testimage'
fails when expected.

As an example, I used 'bitbake core-image-ptest-util-linux:do_testimage'.
It succeeded with warning message. I didn't notice the warning message.
I saw the command succeeded and I tought util-linux ptest is OK. But
in actual fact, the ptest failed. It's the PTEST_EXPECT_FAILURE setting
in this core-image-ptest.bb that is not giving me error.

With this change, I can put PTEST_EXPECT_FAILURE = "1" in my local.conf,
and I can easily see if 'core-image-ptest-xxx:do_testimage' succeeds or
not.

The PTEST_EXPECT_FAILURE change should result in testdata regenerated
because ptest.py test case's behavior is affected by it.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
---
 meta/recipes-core/images/core-image-ptest.bb | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/meta/recipes-core/images/core-image-ptest.bb b/meta/recipes-core/images/core-image-ptest.bb
index 017f05f81b..b554964d20 100644
--- a/meta/recipes-core/images/core-image-ptest.bb
+++ b/meta/recipes-core/images/core-image-ptest.bb
@@ -42,7 +42,8 @@ QB_MEM:virtclass-mcextend-tcl = "-m 5100"
 TEST_SUITES = "ping ssh parselogs ptest"
 
 # Sadly at the moment the full set of ptests is not robust enough and sporadically fails in random places
-PTEST_EXPECT_FAILURE = "1"
+PTEST_EXPECT_FAILURE ?= "1"
+write_image_test_data[vardeps] += "PTEST_EXPECT_FAILURE"
 
 python () {
     if not d.getVar("MCNAME"):
-- 
2.43.0