Fix distutils’ check and register Unicode handling (#13114).

Fix distutils’ check and register Unicode handling (#13114).

The check command was fixed by Kirill Kuzminykh.

The register command was using StringIO.getvalue, which uses “''.join”
and thus coerces to str using the default encoding (ASCII), so I changed
the code to use one extra intermediary list and correctly encode to
UTF-8.