Disable flaky GuestSessionRlzTest/GuestSessionRlzTest.DeviceIsLocked/0

E.g.
https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-google-rel/6929

[1756:1756:0922/124740.991289:ERROR:browser_context.cc(300)] Ignoring request for unknown per-browser-context service:multidevice_setup
../../chrome/browser/chromeos/login/session/chrome_session_manager_browsertest.cc:295: Failure
Expected equality of these values:
  expected_brand
    Which is: ""
  google_brand::chromeos::GetBrand()
    Which is: "TEST"
Stack trace:

[1756:1756:0922/124741.053454:INFO:rlz_tracker.cc(306)] RLZ is disabled
[  FAILED  ] GuestSessionRlzTest/GuestSessionRlzTest.DeviceIsLocked/0, where GetParam() = false (664 ms)

TBR=rogerta@chromium.org

Bug: 997360
Change-Id: I020c643d74107e0ee811f829bfea3a8f75400d5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1817864Reviewed-by: Trent Apted <tapted@chromium.org>
Commit-Queue: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#698802}

chrome/browser/chromeos/login/session/chrome_session_manager_browsertest.cc

@@ -289,7 +289,8 @@ class GuestSessionRlzTest : public InProcessBrowserTest,
   DISALLOW_COPY_AND_ASSIGN(GuestSessionRlzTest);
 };
 
-IN_PROC_BROWSER_TEST_P(GuestSessionRlzTest, DeviceIsLocked) {
+// Flaky. https://crbug.com/997360.
+IN_PROC_BROWSER_TEST_P(GuestSessionRlzTest, DISABLED_DeviceIsLocked) {
   const char* const expected_brand =
       stub_install_attributes()->IsDeviceLocked() ? "TEST" : "";
   EXPECT_EQ(expected_brand, google_brand::chromeos::GetBrand());