oeqa/selftest/wic: Use a subdir of builddir, not /var/

Using /var/ leave wic open to races with other processes on the system, use
a subdir of builddir instead to avoid this.

(From OE-Core rev: e07ec908ce7f26143a7bdf0a07a1230c0fd6ac87)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

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

@@ -64,13 +64,13 @@ def only_for_arch(archs, image='core-image-minimal'):
 class Wic(OESelftestTestCase):
     """Wic test class."""
 
-    resultdir = "/var/tmp/wic.oe-selftest/"
     image_is_ready = False
     native_sysroot = None
     wicenv_cache = {}
 
     def setUpLocal(self):
         """This code is executed before each test method."""
+        self.resultdir = self.builddir + "/wic-tmp/"
         super(Wic, self).setUpLocal()
         if not self.native_sysroot:
             Wic.native_sysroot = get_bb_var('STAGING_DIR_NATIVE', 'wic-tools')