[test] Prepare switching full-debug builder to swarming

NOTRY=true
TBR=sergiyb@chromium.org

Bug: chromium:830557
Change-Id: I2dd9e040c0d29a49aa0a23283da67d550a110677
Reviewed-on: https://chromium-review.googlesource.com/c/1296453Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56894}

infra/testing/builders.pyl

@@ -620,8 +620,13 @@
     ],
   },
   'V8 Linux - full debug': {
+    'swarming_task_attrs': {
+      'expiration': 14400,
+      'hard_timeout': 3600,
+      'priority': 35,
+    },
     'tests': [
-      {'name': 'v8testing', 'variant': 'default'},
+      {'name': 'v8testing', 'variant': 'default', 'shards': 2},
     ],
   },
   'V8 Linux - gc stress': {