po: rewrite the way how we generate files

po: rewrite the way how we generate files

There was no need to handle files for translation from build directory
but that will change with following patches where we will stop
generating source files into source directory.

In order to have them included for translation we have to prefix each
file with SRCDIR or BUILDDIR.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>