Override 'shards' param from json.

Fixed ios13-beta build by adding shards:1 because
test_runner does not support multi-sharding command
https://chromium-swarm.appspot.com/task?id=46388c76bc6f6410

Change-Id: I426b3ecc8790508656b31ac9f6fbf7d54245ff92
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1715565Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Mike Dougherty <michaeldo@chromium.org>
Commit-Queue: Maksym Onufriienko <monufriienko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680174}

ios/build/bots/chromium.fyi/ios13-beta-simulator.json

@@ -87,7 +87,7 @@
       }
     },
     {
-      "xcode parallelization": false,
+      "shards": 1,
       "include": "eg_cq_tests.json",
       "device type": "iPhone X",
       "os": "13.0",
@@ -101,7 +101,7 @@
       }
     },
     {
-      "xcode parallelization": false,
+      "shards": 1,
       "include": "eg_cq_tests.json",
       "device type": "iPad Pro (12.9-inch)",
       "os": "13.0",
@@ -115,7 +115,7 @@
       }
     },
     {
-      "xcode parallelization": false,
+      "shards": 1,
       "include": "eg_tests.json",
       "device type": "iPhone X",
       "os": "13.0",
@@ -129,7 +129,7 @@
       }
     },
     {
-      "xcode parallelization": false,
+      "shards": 1,
       "include": "eg_tests.json",
       "device type": "iPad Air (3rd generation)",
       "os": "13.0",

ios/build/bots/scripts/run.py

@@ -290,6 +290,7 @@ def parse_args():
   args.xctest = args_json.get('xctest', args.xctest)
   args.xcode_parallelization = args_json.get('xcode_parallelization',
                                              args.xcode_parallelization)
+  args.shards = args_json.get('shards', args.shards)
   test_args.extend(args_json.get('test_args', []))
 
   return args, test_args