Make bucket names explicit in cq.cfg.

Don't assume bucket name to start with 'master.'.

NOTRY=True
BUG=chromium:617627
R=machenbach@chromium.org

Review-Url: https://codereview.chromium.org/2093993002
Cr-Commit-Position: refs/heads/master@{#37258}

infra/config/cq.cfg

@@ -25,7 +25,7 @@ verifiers {
 
   try_job {
     buckets {
-      name: "tryserver.v8"
+      name: "master.tryserver.v8"
       builders { name: "v8_android_arm_compile_rel" }
       builders { name: "v8_linux64_asan_rel_ng" }
       builders {