Bug 1601500, 1601497 - mark failing grid-container-scrollbar-vertical tests with expected failure for ubuntu1804 r=jmaher

Changes:

These tests have no clearly defined owners - the person that worked on this doesn't even have a last active date. We've seen, in other reftests, scrollbar related pixel differences so I'm inclined to believe that also plays a role here.

Mark these tests as expected failures on ubuntu1804.

Differential Revision: https://phabricator.services.mozilla.com/D57901

--HG--
extra : moz-landing-system : lando

testing/web-platform/meta/css/css-grid/grid-model/grid-container-scrollbar-vertical-lr-001.html.ini

@@ -1,3 +1,4 @@
 [grid-container-scrollbar-vertical-lr-001.html]
   expected:
     if os == "mac": FAIL
+    if (os == 'linux' and os_version == '18.04'): FAIL # Bug 1601497

testing/web-platform/meta/css/css-grid/grid-model/grid-container-scrollbar-vertical-rl-001.html.ini

@@ -1,3 +1,4 @@
 [grid-container-scrollbar-vertical-rl-001.html]
   expected:
     if os == "mac": FAIL
+    if (os == 'linux' and os_version == '18.04'): FAIL # Bug 1601500