WebRTC: Add iOS bots running tests with the simulator

scripts/slave/recipes/ios/try.expected/gn.json

 [
   {
     "cmd": [
       "[BUILD]/scripts/slave/ios/host_info.py",
       "--json-file",
       "/path/to/tmp/json"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "host and tools info",
     "~followup_annotations": [
@@ skipping 139 matching lines @@
       "@@@STEP_LOG_LINE@json.output@  ], @@@",
       "@@@STEP_LOG_LINE@json.output@  \"xcode version\": \"fake xcode version\"@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "cmd": [
       "echo",
       "-e",
-      "{\n  \"GYP_DEFINES\": [], \n  \"additional_compile_targets\": [\n    \"All\"\n  ], \n  \"compiler\": \"ninja\", \n  \"configuration\": \"Debug\", \n  \"env\": {}, \n  \"gn_args\": [\n    \"target_os=\\\"ios\\\"\", \n    \"ios_enable_code_signing=false\", \n    \"use_goma=true\"\n  ], \n  \"mb_type\": \"gn\", \n  \"sdk\": \"iphonesimulator8.0\", \n  \"tests\": [\n    {\n      \"app\": \"fake tests\", \n      \"device type\": \"fake device\", \n      \"os\": \"8.1\"\n    }\n  ], \n  \"triggered bots\": {}, \n  \"xcode version\": \"fake xcode version\"\n}"
+      "{\n  \"GYP_DEFINES\": [], \n  \"additional_compile_targets\": [\n    \"All\"\n  ], \n  \"compiler\": \"ninja\", \n  \"configuration\": \"Debug\", \n  \"env\": {}, \n  \"gn_args\": [\n    \"target_os=\\\"ios\\\"\", \n    \"ios_enable_code_signing=false\", \n    \"use_goma=true\"\n  ], \n  \"mb_type\": \"gn\", \n  \"sdk\": \"iphonesimulator8.0\", \n  \"tests\": [\n    {\n      \"app\": \"fake tests\", \n      \"device type\": \"fake device\", \n      \"os\": \"8.1\"\n    }\n  ], \n  \"triggered bots\": {}, \n  \"use_analyze\": true, \n  \"xcode version\": \"fake xcode version\"\n}"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "finalize build config"
   },
   {
     "cmd": [
       "[BUILD]/scripts/slave/ios/find_xcode.py",
       "--json-file",
       "/path/to/tmp/json",
       "--version",
@@ skipping 206 matching lines @@
       "@@@STEP_LOG_END@fake log@@@",
       "@@@STEP_LINK@fake URL text@fake URL@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]