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

scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___arm64___sim___nosnap___debug.json

Index: scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___arm64___sim___nosnap___debug.json
diff --git a/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___arm64___sim___nosnap___debug.json b/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___arm64___sim___nosnap___debug.json
index 23bd68ad6ed7b6aa7b8115ee641150d571c61509..ee74a5eeb8c3dc60fe9615849be4f3d0bd531f55 100644
--- a/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___arm64___sim___nosnap___debug.json
+++ b/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___arm64___sim___nosnap___debug.json
@@ -235,7 +235,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Check",
+      "stepname:Check on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for bot_default]",
       "--",
@@ -258,7 +258,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Check",
+    "name": "[trigger] Check on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Check/Ubuntu-12.04/[dummy has/V8 Linux - arm64 - sim - nosnap - debug/571\", @@@",
@@ -349,7 +349,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Test262 - no variants",
+      "stepname:Test262 - no variants on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for test262]",
       "--",
@@ -374,7 +374,7 @@
       "${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 - arm64 - sim - nosnap - debug/571\", @@@",
@@ -453,7 +453,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:Mozilla",
+      "stepname:Mozilla on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for mozilla]",
       "--",
@@ -476,7 +476,7 @@
       "${ISOLATED_OUTDIR}/output.json"
     ],
     "cwd": "[SLAVE_BUILD]",
-    "name": "[trigger] Mozilla",
+    "name": "[trigger] Mozilla on Ubuntu-12.04",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"base_task_name\": \"Mozilla/Ubuntu-12.04/[dummy has/V8 Linux - arm64 - sim - nosnap - debug/571\", @@@",
@@ -549,7 +549,7 @@
       "--tag",
       "slavename:TestSlavename",
       "--tag",
-      "stepname:SimdJs - all",
+      "stepname:SimdJs - all on Ubuntu-12.04",
       "--idempotent",
       "[dummy hash for simdjs]",
       "--",
@@ -573,7 +573,7 @@
       "${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 - arm64 - sim - nosnap - debug/571\", @@@",