Make all shell scripts using /bin/bash instead /bin/sh to be able to FAI's environment.

/usr/lib/fai/subroutines sadly is a /bin/bash script.
As we want to be able to use functions like ifclass
we have to use /bin/bash in all our scripts (even
though they're POSIX ones), otherwise people
using dash as /bin/sh will notice something like:

  /GRMLBASE/25-locales: 23: ifclass: not found

in their FAI's shell.log.

Thanks: thermoman
Signed-off-by: Michael Prokop <mika@grml.org>