oeqa/selftest/esdk: run selftest inside workdir not /tmp

We've seen issues with rootfs size calculations and we've seen systems
like opensuse which have btrfs mounted on /tmp causing selftest failures.

(From OE-Core rev: 61be3cd748d1b7321a1fc4cfe84efa9b26a6aee0)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/selftest/cases/eSDK.py

@@ -70,11 +70,12 @@ CORE_IMAGE_EXTRA_INSTALL = "perl"
     @classmethod
     def setUpClass(cls):
         super(oeSDKExtSelfTest, cls).setUpClass()
-        cls.tmpdir_eSDKQA = tempfile.mkdtemp(prefix='eSDKQA')
-
-        sstate_dir = get_bb_var('SSTATE_DIR')
-
         cls.image = 'core-image-minimal'
+
+        bb_vars = get_bb_vars(['SSTATE_DIR', 'WORKDIR'], cls.image)
+        cls.tmpdirobj = tempfile.TemporaryDirectory(prefix="selftest-esdk-", dir=bb_vars["WORKDIR"])
+        cls.tmpdir_eSDKQA = cls.tempdirobj.name
+
         oeSDKExtSelfTest.generate_eSDK(cls.image)
 
         # Install eSDK
@@ -87,14 +88,14 @@ CORE_IMAGE_EXTRA_INSTALL = "perl"
         sstate_config="""
 SDK_LOCAL_CONF_WHITELIST = "SSTATE_MIRRORS"
 SSTATE_MIRRORS =  "file://.* file://%s/PATH"
-            """ % sstate_dir
+            """ % bb_vars["SSTATE_DIR"]
         with open(os.path.join(cls.tmpdir_eSDKQA, 'conf', 'local.conf'), 'a+') as f:
             f.write(sstate_config)
 
     @classmethod
     def tearDownClass(cls):
-        shutil.rmtree(cls.tmpdir_eSDKQA, ignore_errors=True)
-        super(oeSDKExtSelfTest, cls).tearDownClass()
+        cls.tmpdirobj.cleanup()
+        super().tearDownClass()
 
     @OETestID(1602)
     def test_install_libraries_headers(self):