Bug 1859676 - Port bug 1857516: Add mozfile to tb_common.txt mach site. r=darktrojan

It's needed to import mach.command_util now. The mach site cannot be initialzed
twice.

Differential Revision: https://phabricator.services.mozilla.com/D191256

--HG--
extra : moz-landing-system : lando

build/mach_initialize.py

@@ -25,6 +25,7 @@ def mach_sys_path(mozilla_dir):
             os.path.join("python", "mach"),
             os.path.join("third_party", "python", "packaging"),
             os.path.join("third_party", "python", "pyparsing"),
+            os.path.join("third_party", "python", "six"),
         )
     ]
     from mach.requirements import MachEnvRequirements

python/sites/tb_common.txt

@@ -4,6 +4,7 @@ pth:comm/python/thirdroc
 pth:comm/taskcluster
 pth:comm/testing/marionette
 vendored:comm/third_party/python/fluent.migratetb
+pth:testing/mozbase/mozfile
 vendored:third_party/python/compare_locales
 vendored:third_party/python/fluent.migrate
 vendored:third_party/python/fluent.syntax