scripts: update open calls to use explicit encoding

BUG=b:187789896
TEST=`cros lint` is clean here

Change-Id: Ia54475869c17292505537334362cd4cff6438b14
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4290041
Commit-Queue: Cindy Lin <xcl@google.com>
Reviewed-by: Cindy Lin <xcl@google.com>
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index 8138193..ddd7f52 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -150,8 +150,8 @@
         "branch": options.branch,
     }
     if options.metadata_dump:
-        with open(options.metadata_dump, "r") as metadata_file:
-            metadata_dump_dict = json.loads(metadata_file.read())
+        with open(options.metadata_dump, "rb") as metadata_file:
+            metadata_dump_dict = json.load(metadata_file)
 
     with parallel.Manager() as manager:
         builder_run = cbuildbot_run.BuilderRun(
@@ -1229,7 +1229,7 @@
         stack.Add(critical_section.ForkWatchdog)
 
         if options.mock_slave_status is not None:
-            with open(options.mock_slave_status, "r") as f:
+            with open(options.mock_slave_status, "rb") as f:
                 mock_statuses = pickle.load(f)
                 for key, value in mock_statuses.items():
                     mock_statuses[key] = builder_status_lib.BuilderStatus(