properly setup locale in installation start script (bnc#902411)

to display texts and labels correctly in a texmode installation and also to
translate all buttons in graphical mode (removed "testutf8" calls, it has been
dropped, always set UTF-8 locale)

- 3.1.117
Merge pull request #240 from yast/remove_testutf8

properly setup locale in installation start script (bnc#902411)