ios: Allow bot configs to set extra env variables

scripts/slave/recipes/ios/unified_builder_tester.expected/basic.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 85 matching lines @@
     "cwd": "[SLAVE_BUILD]",
     "name": "read build config",
     "~followup_annotations": [
       "@@@STEP_LOG_LINE@json.output@{@@@",
       "@@@STEP_LOG_LINE@json.output@  \"GYP_DEFINES\": {@@@",
       "@@@STEP_LOG_LINE@json.output@    \"fake gyp define 1\": \"fake value 1\", @@@",
       "@@@STEP_LOG_LINE@json.output@    \"fake gyp define 2\": \"fake value 2\"@@@",
       "@@@STEP_LOG_LINE@json.output@  }, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"compiler\": \"xcodebuild\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"configuration\": \"Debug\", @@@",
+      "@@@STEP_LOG_LINE@json.output@  \"env\": {@@@",
+      "@@@STEP_LOG_LINE@json.output@    \"fake env var 1\": \"fake env value 1\", @@@",
+      "@@@STEP_LOG_LINE@json.output@    \"fake env var 2\": \"fake env value 2\"@@@",
+      "@@@STEP_LOG_LINE@json.output@  }, @@@",
       "@@@STEP_LOG_LINE@json.output@  \"sdk\": \"iphonesimulator8.0\", @@@",
       "@@@STEP_LOG_LINE@json.output@  \"tests\": [@@@",
       "@@@STEP_LOG_LINE@json.output@    {@@@",
       "@@@STEP_LOG_LINE@json.output@      \"app\": \"fake tests 1\", @@@",
       "@@@STEP_LOG_LINE@json.output@      \"device type\": \"fake device\", @@@",
       "@@@STEP_LOG_LINE@json.output@      \"os\": \"8.0\"@@@",
       "@@@STEP_LOG_LINE@json.output@    }, @@@",
       "@@@STEP_LOG_LINE@json.output@    {@@@",
       "@@@STEP_LOG_LINE@json.output@      \"app\": \"fake tests 2\", @@@",
       "@@@STEP_LOG_LINE@json.output@      \"device type\": \"fake device\", @@@",
       "@@@STEP_LOG_LINE@json.output@      \"os\": \"7.1\"@@@",
       "@@@STEP_LOG_LINE@json.output@    }@@@",
       "@@@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    \"OS\": \"ios\", \n    \"component\": \"static_library\", \n    \"fake gyp define 1\": \"fake value 1\", \n    \"fake gyp define 2\": \"fake value 2\"\n  }, \n  \"compiler\": \"xcodebuild\", \n  \"configuration\": \"Debug\", \n  \"sdk\": \"iphonesimulator8.0\", \n  \"tests\": [\n    {\n      \"app\": \"fake tests 1\", \n      \"device type\": \"fake device\", \n      \"os\": \"8.0\"\n    }, \n    {\n      \"app\": \"fake tests 2\", \n      \"device type\": \"fake device\", \n      \"os\": \"7.1\"\n    }\n  ], \n  \"triggered bots\": {}, \n  \"xcode version\": \"fake xcode version\"\n}"
+      "{\n  \"GYP_DEFINES\": {\n    \"OS\": \"ios\", \n    \"component\": \"static_library\", \n    \"fake gyp define 1\": \"fake value 1\", \n    \"fake gyp define 2\": \"fake value 2\"\n  }, \n  \"compiler\": \"xcodebuild\", \n  \"configuration\": \"Debug\", \n  \"env\": {\n    \"fake env var 1\": \"fake env value 1\", \n    \"fake env var 2\": \"fake env value 2\"\n  }, \n  \"sdk\": \"iphonesimulator8.0\", \n  \"tests\": [\n    {\n      \"app\": \"fake tests 1\", \n      \"device type\": \"fake device\", \n      \"os\": \"8.0\"\n    }, \n    {\n      \"app\": \"fake tests 2\", \n      \"device type\": \"fake device\", \n      \"os\": \"7.1\"\n    }\n  ], \n  \"triggered bots\": {}, \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 11 matching lines @@
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_DEFINES": "fake gyp define 1=fake value 1 fake gyp define 2=fake value 2 component=static_library OS=ios",
       "GYP_GENERATORS": "xcode",
       "GYP_GENERATOR_FLAGS": "xcode_project_version=3.2",
-      "LANDMINES_VERBOSE": "1"
+      "LANDMINES_VERBOSE": "1",
+      "fake env var 1": "fake env value 1",
+      "fake env var 2": "fake env value 2"
     },
     "name": "gclient runhooks",
     "~followup_annotations": [
       "@@@STEP_TEXT@<br />GYP_DEFINES:<br />fake gyp define 1=fake value 1<br />fake gyp define 2=fake value 2<br />component=static_library<br />OS=ios@@@"
     ]
   },
   {
     "cmd": [
       "xcodebuild",
       "-configuration",
@@ skipping 70 matching lines @@
       "@@@STEP_LOG_LINE@json.output@  }@@@",
       "@@@STEP_LOG_LINE@json.output@}@@@",
       "@@@STEP_LOG_END@json.output@@@",
       "@@@STEP_LOG_LINE@fake log@fake log line 1@@@",
       "@@@STEP_LOG_LINE@fake log@fake log line 2@@@",
       "@@@STEP_LOG_END@fake log@@@",
       "@@@STEP_LINK@fake URL text@fake URL@@@"
     ]
   }
 ]