Add host os: to the ipad air 2 and 6th gen runs.

Bug: 1012488
Change-Id: Ie6a758ea7e90d8f023c9dfc766737e20996157bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1848791Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Lindsay Pasricha <lindsayw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704051}

ios/build/bots/chromium.mac/ios-simulator-noncq.json

@@ -78,7 +78,8 @@
       "device type": "iPad (6th generation)",
       "os": "12.2",
       "xcode build version": "11a420a",
-      "pool":"Chrome"
+      "pool":"Chrome",
+      "host os": "Mac-10.14.6"
     },
     {
       "xcode parallelization": true,
@@ -86,7 +87,8 @@
       "device type": "iPad Air 2",
       "os": "12.2",
       "xcode build version": "11a420a",
-      "pool":"Chrome"
+      "pool":"Chrome",
+      "host os": "Mac-10.14.6"
     }
   ]
 }