swarming: only use text until first space for name tag

scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___nosnap___debug.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::git]/resources/git_setup.py",
       "--path",
       "[SLAVE_BUILD]/swarming.client",
       "--url",
       "https://chromium.googlesource.com/external/swarming.client.git"
@@ skipping 325 matching lines @@
       "Chrome",
       "--tag",
       "buildername:V8 Linux - nosnap - debug",
       "--tag",
       "buildnumber:571",
       "--tag",
       "data:[dummy hash for simdjs]",
       "--tag",
       "master:client.v8",
       "--tag",
-      "name:SimdJs - all",
+      "name:SimdJs",
       "--tag",
       "os:Ubuntu-12.04",
       "--tag",
       "project:v8",
       "--tag",
       "purpose:CI",
       "--tag",
       "purpose:post-commit",
       "--tag",
       "slavename:TestSlavename",
@@ skipping 160 matching lines @@
       "@@@STEP_LOG_LINE@durations@Duration: 00:00:101@@@",
       "@@@STEP_LOG_END@durations@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]