Execute the script using python api module.

scripts/slave/recipes/bisection/desktop_bisect.expected/basic.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[BUILD]/scripts/slave/bot_update.py",
       "--master",
       "tryserver.chromium.perf",
       "--builder",
       "linux_perf_bisect",
@@ skipping 64 matching lines @@
       "runhooks"
     ],
     "cwd": "[SLAVE_BUILD]",
     "env": {
       "GYP_DEFINES": "branding=Chrome buildtype=Official component=static_library gomadir='[BUILD]/goma' target_arch=x64 use_goma=1"
     },
     "name": "gclient runhooks (with patch)"
   },
   {
     "cmd": [
+      "python",
+      "-u",
       "[SLAVE_BUILD]/src/tools/prepare-bisect-perf-regression.py",
       "-w",
       "[SLAVE_BUILD]"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "Preparing for Bisection"
   },
   {
     "allow_subannotations": true,
     "cmd": [
@@ skipping 17 matching lines @@
       "[SLAVE_BUILD]",
       "--path_to_goma",
       "[BUILD]/goma",
       "--build-properties",
       "{\"blamelist\": [\"cool_dev1337@chromium.org\", \"hax@chromium.org\"], \"branch\": \"\", \"buildername\": \"linux_perf_bisect\", \"buildnumber\": 571, \"issue\": 12853011, \"mastername\": \"tryserver.chromium.perf\", \"patch_project\": \"chromium\", \"patchset\": 1, \"project\": \"chrome\", \"recipe\": \"bisection/desktop_bisect\", \"repository\": \"\", \"requester\": \"commit-bot@chromium.org\", \"revision\": \"HEAD\", \"rietveld\": \"https://codereview.chromium.org\", \"slavename\": \"TestSlavename\", \"workdir\": \"/path/to/workdir/TestSlavename\"}"
     ],
     "cwd": "[SLAVE_BUILD]",
     "name": "Running Bisection"
   }
 ]