[catapult] fix file open issue in py3 migration in add reserved diagnostics
[catapult] fix file open issue in py3 migration in add reserved diagnostics

Bug: chromium:967125
Change-Id: Ib0ac92327ab26204599a1990095b7636fa8cd52d
Reviewed-on: https://chromium-review.googlesource.com/c/catapult/+/3646595
Commit-Queue: Wenbin Zhang <45ad8a1ff616a38a2202fd35571df81897c5f14f@google.com>
Reviewed-by: John Chen <334fbfbb4df7c78f091ea1b77c69ca6ac731a3f3@chromium.org>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult