Do not randomize chosen locale and use a UTF-8 supported locale.

(Closes: #925879, #1004950)

Use an Estonian locale, which has unusual sort order compared to many
european languages, which may catch some interesting issues.

Testing more obscure locales and character sets is certainly
desireable, but it is also very important for reprotest to pick the
varied locale deterministically.

Randomly choosing the locale, or choosing based on a hash of the
inputs, might lead to picking a different locale while debugging
patches for a potential fix, with misleading results if the issue is
highly locale specific.