Set android_browser_finder.psutil to None in...

Set android_browser_finder.psutil to None in tools/telemetry/telemetry/core/backends/chrome/android_browser_finder_unittest.py to avoid flakiness

BUG=426604

Review URL: https://codereview.chromium.org/667423003

Cr-Commit-Position: refs/heads/master@{#302736}

tools/telemetry/telemetry/core/backends/chrome/android_browser_finder_unittest.py

@@ -21,11 +21,14 @@ class AndroidBrowserFinderTest(unittest.TestCase):
         android_device, ['adb_commands'])
     self._apb_stub = system_stub.Override(
         android_platform_backend, ['adb_commands'])
+    self._actual_ps_util = android_browser_finder.psutil
+    android_browser_finder.psutil = None
 
   def tearDown(self):
     self._stubs.Restore()
     self._android_device_stub.Restore()
     self._apb_stub.Restore()
+    android_browser_finder.psutil = self._actual_ps_util
 
   def test_no_adb(self):
     finder_options = browser_options.BrowserFinderOptions()