swarming: always append task's OS dimension to step name

scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_arm_armv8a_dbg.json

Index: scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_arm_armv8a_dbg.json
diff --git a/scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_arm_armv8a_dbg.json b/scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_arm_armv8a_dbg.json
index 36c345a90ebf785cb37c9237e9791982db2b9c13..61d9c7d3961b5cb300b65330f9ab09a1a8472efb 100644
--- a/scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_arm_armv8a_dbg.json
+++ b/scripts/slave/recipes/v8.expected/full_tryserver_v8_v8_linux_arm_armv8a_dbg.json
@@ -247,7 +247,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Check",
+      "stepname:Check on Ubuntu-12.04",
       "--idempotent",
       "--user",
       "commit-bot@chromium.org",
@@ -274,7 +274,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Check",
+    "name": "[trigger] Check on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Check/Ubuntu-12.04/[dummy has/v8_linux_arm_armv8a_dbg/571\", @@@",
@@ -363,7 +363,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Test262 - no variants",
+      "stepname:Test262 - no variants on Ubuntu-12.04",
       "--idempotent",
       "--user",
       "commit-bot@chromium.org",
@@ -392,7 +392,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Test262 - no variants",
+    "name": "[trigger] Test262 - no variants on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Test262 - no variants/Ubuntu-12.04/[dummy has/v8_linux_arm_armv8a_dbg/571\", @@@",
@@ -469,7 +469,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Mozilla",
+      "stepname:Mozilla on Ubuntu-12.04",
       "--idempotent",
       "--user",
       "commit-bot@chromium.org",
@@ -496,7 +496,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Mozilla",
+    "name": "[trigger] Mozilla on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Mozilla/Ubuntu-12.04/[dummy has/v8_linux_arm_armv8a_dbg/571\", @@@",
@@ -573,7 +573,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:SimdJs - all",
+      "stepname:SimdJs - all on Ubuntu-12.04",
       "--idempotent",
       "--user",
       "commit-bot@chromium.org",
@@ -601,7 +601,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] SimdJs - all",
+    "name": "[trigger] SimdJs - all on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"SimdJs - all/Ubuntu-12.04/[dummy has/v8_linux_arm_armv8a_dbg/571\", @@@",