constants: convert CHROMITE_DIR to a Path object

BUG=None
TEST=CQ passes

Change-Id: I826e6fcddcd205435c65df69b030caf43ea3ab29
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4358397
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Ram Chandrasekar <rchandrasekar@google.com>
diff --git a/api/controller/api_unittest.py b/api/controller/api_unittest.py
index ebf03e5..29c31f8 100644
--- a/api/controller/api_unittest.py
+++ b/api/controller/api_unittest.py
@@ -4,8 +4,6 @@
 
 """API controller tests."""
 
-import os
-
 from chromite.api import api_config
 from chromite.api import router
 from chromite.api.controller import api as api_controller
@@ -26,7 +24,7 @@
     def testCompileProto(self):
         """Quick CompileProto functional check."""
         self.rc.SetDefaultCmdResult(stdout=" M foo/bar.py")
-        expected = [os.path.join(constants.CHROMITE_DIR, "foo/bar.py")]
+        expected = [str(constants.CHROMITE_DIR / "foo" / "bar.py")]
 
         api_controller.CompileProto(
             self.request, self.response, self.api_config