servo: Merge #7117 - Reenable "Use one Python virtual environment for all mach commands" (from frewsxcv:python-venv); r=jdm

Address the issues brought up by https://github.com/servo/servo/pull/7103

The revert requires an upgrade to wptrunner (for the mozlog 3.0 compatibility) because the latest wptrunner depends on [this](https://github.com/w3c/wpt-tools/pull/27))

/cc @Ms2ger @metajack

Source-Repo: https://github.com/servo/servo
Source-Revision: 4e6bbe227299b3b8a08cba7e613952806ada4402

servo/python/tidy.py

@@ -19,23 +19,15 @@ from licenseck import licenses
 filetypes_to_check = [".rs", ".rc", ".cpp", ".c", ".h", ".lock", ".py", ".toml", ".webidl"]
 reftest_dir = "./tests/ref"
 reftest_filetype = ".list"
-python_dependencies = [
-    "./python/dependencies/flake8-2.4.1-py2.py3-none-any.whl",
-    "./python/dependencies/pep8-1.5.7-py2.py3-none-any.whl",
-    "./python/dependencies/pyflakes-0.9.0-py2.py3-none-any.whl",
-]
 
 ignored_files = [
     # Upstream
     "./support/*",
     "./tests/wpt/*",
     "./python/mach/*",
-    "./python/mozdebug/*",
-    "./python/mozinfo/*",
-    "./python/mozlog/*",
-    "./python/toml/*",
     "./components/script/dom/bindings/codegen/parser/*",
     "./components/script/dom/bindings/codegen/ply/*",
+    "./python/_virtualenv/*",
 
     # Generated and upstream code combined with our own. Could use cleanup
     "./target/*",
@@ -418,7 +410,6 @@ def check_spec(file_name, contents):
 
 
 def collect_errors_for_files(files_to_check, checking_functions):
-    base_path = "components/script/dom/"
     for file_name in files_to_check:
         with open(file_name, "r") as fp:
             contents = fp.read()
@@ -467,8 +458,6 @@ def check_reftest_html_files_in_basic_list(reftest_dir):
 
 
 def scan():
-    sys.path += python_dependencies
-
     all_files = (os.path.join(r, f) for r, _, files in os.walk(".") for f in files)
     files_to_check = filter(should_check, all_files)