In Addition to #206, generate the locals before change to it.

For my german box changing the locale failed:
´´´´/bin/sh: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
/bin/sh: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
/bin/sh: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
/bin/sh: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)
setup/functions.sh: line 6: warning: setlocale: LC_ALL: cannot change locale (en_US.UTF-8)´´´´

The first use / change happens in [function.sh](https://github.com/mail-in-a-box/mailinabox/blob/master/setup/functions.sh#L5) so in my opinion we have to generate it in bootstrap.sh.