mac: Make cross-platform hermetic download work with both py2 and py3.

Follow-up to https://chromium-review.googlesource.com/c/2277455

Bug: 1098899,1147069
Change-Id: I240ea9caf53a62a632376fed45b0e488758c1305
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2526924
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Auto-Submit: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825377}

build/mac/should_use_hermetic_xcode.py

@@ -33,7 +33,8 @@ def _IsCorpMachine():
   if sys.platform.startswith('linux'):
     import subprocess
     try:
-      return subprocess.check_output('lsb_release -sc').rstrip() == 'rodete'
+      return subprocess.check_output(['lsb_release',
+                                      '-sc']).rstrip() == b'rodete'
     except:
       return False
   return False