utils: run commands using utf-8 string on Windows

Summary:

Use unicode string to call commans

Backport of core PR13886
https://github.com/bitcoin/bitcoin/pull/13886/files

Will fix gitian windows build issue introduced in D3241.

Test Plan:

make check

Build for windows:

mkdir buildcmake && cd buildcmake
cmake -GNinja .. -DCMAKE_TOOLCHAIN_FILE=../cmake/platforms/Win64.cmake \
-DBUILD_BITCOIN_SEEDER=OFF
ninja

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D3272