Bug 1482957 - Download minidump_stackwalk in android-hw tests; r=bc

The script was setting minidump_stackwalk_path, signalling that minidump_stackwalk
is expected to be found pre-installed at that location. When the path is not set,
the executable is downloaded.

testing/mozharness/configs/android/android_hw.py

@@ -23,6 +23,7 @@ config = {
     # from android_common.py
     "download_tooltool": True,
     "download_minidump_stackwalk": True,
+    "minidump_stackwalk_path": "linux64-minidump_stackwalk",
     "tooltool_servers": ['https://tooltool.mozilla-releng.net/'],
     # minidump_tooltool_manifest_path is relative to workspace/build/tests/
     "minidump_tooltool_manifest_path": "config/tooltool-manifests/linux64/releng.manifest",

testing/mozharness/scripts/android_hardware_unittest.py

@@ -106,7 +106,6 @@ class AndroidHardwareTest(TestingMixin, BaseScript, MozbaseMixin,
         self.test_packages_url = c.get('test_packages_url')
         self.test_manifest = c.get('test_manifest')
         self.robocop_path = os.path.join(abs_dirs['abs_work_dir'], "robocop.apk")
-        self.minidump_stackwalk_path = c.get("minidump_stackwalk_path")
         self.device_name = os.environ['DEVICE_NAME']
         self.device_serial = os.environ['DEVICE_SERIAL']
         self.device_ip = os.environ['DEVICE_IP']