Fix test-wpt and test-css for Windows.

In addition to minor changes for Windows, this forces Windows Python to
be used for all Windows builds (instead of using Windows Python only for
pc-windows-msvc builds).

tests/wpt/web-platform-tests/tools/sslutils/openssl.py

@@ -57,7 +57,13 @@ class OpenSSL(object):
             self.cmd += ["-config", self.conf_path]
         self.cmd += list(args)
 
-        env = os.environ.copy()
+        # Copy the environment, converting to plain strings. Windows
+        # StartProcess is picky about all the keys/values being plain strings,
+        # but at least in MSYS shells, the os.environ dictionary can be mixed.
+        env = {}
+        for k, v in os.environ.iteritems():
+            env[k.encode("utf8")] = v.encode("utf8")
+
         if self.base_conf_path is not None:
             env["OPENSSL_CONF"] = self.base_conf_path.encode("utf8")