Reland: Use real revision mapping in bot_update module

scripts/slave/recipes/chromium_trybot.expected/compile_failure_linux_bot_update.json

 [
   {
     "abort_on_failure": true,
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "tryserver.chromium",
       "--builder",
       "linux_rel_alt",
       "--slave",
       "slave101-c4",
       "--spec",
       "cache_dir = None\nsolutions = [{'custom_vars': {'googlecode_url': 'svn://svn-mirror.golo.chromium.org/%s', 'nacl_trunk': 'svn://svn-mirror.golo.chromium.org/native_client/trunk', 'sourceforge_url': 'svn://svn-mirror.golo.chromium.org/%(repo)s', 'webkit_trunk': 'svn://svn-mirror.golo.chromium.org/blink/trunk'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}]",
       "--root",
       "src",
+      "--revision_mapping_file",
+      "{\"src\": \"got_revision\", \"src/native_client\": \"got_nacl_revision\", \"src/third_party/WebKit\": \"got_webkit_revision\", \"src/third_party/webrtc\": \"got_webrtc_revision\", \"src/tools/swarm_client\": \"got_swarm_client_revision\", \"src/tools/swarming_client\": \"got_swarming_client_revision\", \"src/v8\": \"got_v8_revision\"}",
       "--issue",
       "12853011",
       "--patchset",
       "1",
       "--output_json",
       "/path/to/tmp/json"
     ],
     "name": "bot_update",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ skipping 133 matching lines @@
       "--builder",
       "linux_rel_alt",
       "--slave",
       "slave101-c4",
       "--spec",
       "cache_dir = None\nsolutions = [{'custom_vars': {'googlecode_url': 'svn://svn-mirror.golo.chromium.org/%s', 'nacl_trunk': 'svn://svn-mirror.golo.chromium.org/native_client/trunk', 'sourceforge_url': 'svn://svn-mirror.golo.chromium.org/%(repo)s', 'webkit_trunk': 'svn://svn-mirror.golo.chromium.org/blink/trunk'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'safesync_url': 'https://build.chromium.org/p/chromium/lkcr-status/lkgr', 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}]",
       "--root",
       "src",
       "--revision",
       "origin/lkcr",
+      "--revision_mapping_file",
+      "{\"src\": \"got_revision\", \"src/native_client\": \"got_nacl_revision\", \"src/third_party/WebKit\": \"got_webkit_revision\", \"src/third_party/webrtc\": \"got_webrtc_revision\", \"src/tools/swarm_client\": \"got_swarm_client_revision\", \"src/tools/swarming_client\": \"got_swarming_client_revision\", \"src/v8\": \"got_v8_revision\"}",
       "--issue",
       "12853011",
       "--patchset",
       "1",
       "--output_json",
       "/path/to/tmp/json"
     ],
     "name": "bot_update - lkcr clobber",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ skipping 111 matching lines @@
       "--builder",
       "linux_rel_alt",
       "--slave",
       "slave101-c4",
       "--spec",
       "cache_dir = None\nsolutions = [{'custom_vars': {'googlecode_url': 'svn://svn-mirror.golo.chromium.org/%s', 'nacl_trunk': 'svn://svn-mirror.golo.chromium.org/native_client/trunk', 'sourceforge_url': 'svn://svn-mirror.golo.chromium.org/%(repo)s', 'webkit_trunk': 'svn://svn-mirror.golo.chromium.org/blink/trunk'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'safesync_url': 'https://build.chromium.org/p/chromium/lkcr-status/lkgr', 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}]",
       "--root",
       "src",
       "--revision",
       "origin/lkcr",
+      "--revision_mapping_file",
+      "{\"src\": \"got_revision\", \"src/native_client\": \"got_nacl_revision\", \"src/third_party/WebKit\": \"got_webkit_revision\", \"src/third_party/webrtc\": \"got_webrtc_revision\", \"src/tools/swarm_client\": \"got_swarm_client_revision\", \"src/tools/swarming_client\": \"got_swarming_client_revision\", \"src/v8\": \"got_v8_revision\"}",
       "--issue",
       "12853011",
       "--patchset",
       "1",
       "--output_json",
       "/path/to/tmp/json"
     ],
     "name": "bot_update - lkcr clobber nuke",
     "~followup_annotations": [
       "@@@STEP_TEXT@Some step text@@@",
@@ skipping 72 matching lines @@
       "browser_tests",
       "chrome"
     ],
     "name": "compile (with patch, lkcr, clobber, nuke)",
     "~followup_annotations": [
       "step returned non-zero exit code: 1",
       "@@@STEP_FAILURE@@@"
     ]
   }
 ]