support/scripts/genimage.sh: add shell option -e

The commit 6889056f1e (support/scripts/genimage.sh) adds support for
creating bmap images.

Since then, the script genimage.sh looses the error returned by the
genimage command.

As a consequence, the target-finalize target looses the error as well,
and so on up to make.

This adds the shell option -e to exit immediately if a command ends with
an error, so the error is not ignored.

Fixes:

	gportay@archlinux ~/src/rtone-br2-external $ make
	(...)
	>>>   Executing post-image script support/scripts/genimage.sh
	INFO: cmd: "mkdir -p "/home/gportay/src/rtone-br2-external/output/build/genimage.tmp"" (stderr):
	INFO: cmd: "rm -rf "/home/gportay/src/rtone-br2-external/output/build/genimage.tmp"/*" (stderr):
	INFO: cmd: "mkdir -p "/home/gportay/src/rtone-br2-external/output/build/genimage.tmp"" (stderr):
	INFO: cmd: "cp -a "/tmp/tmp.EclKGwtA4R" "/home/gportay/src/rtone-br2-external/output/build/genimage.tmp/root"" (stderr):
	INFO: cmd: "mkdir -p "/home/gportay/src/rtone-br2-external/output/images"" (stderr):
	INFO: vfat(efi-part.vfat): cmd: "mkdosfs   '/home/gportay/src/rtone-br2-external/output/images/efi-part.vfat'" (stderr):
	INFO: vfat(efi-part.vfat): adding file 'efi-part/EFI' as 'EFI' ...
	INFO: vfat(efi-part.vfat): cmd: "MTOOLS_SKIP_CHECK=1 mcopy -sp -i '/home/gportay/src/rtone-br2-external/output/images/efi-part.vfat' '/home/gportay/src/rtone-br2-external/output/images/efi-part/EFI' '::EFI'" (stderr):
	Disk full
	INFO: vfat(efi-part.vfat): cmd: "rm -f "/home/gportay/src/rtone-br2-external/output/images/efi-part.vfat"" (stderr):
	ERROR: vfat(efi-part.vfat): failed to generate efi-part.vfat
	INFO: cmd: "rm -rf "/home/gportay/src/rtone-br2-external/output/build/genimage.tmp/"" (stderr):
	make[1]: Leaving directory '/home/gportay/src/rtone-br2-external/buildroot'
	gportay@archlinux ~/src/rtone-br2-external $ echo $?
	0

Signed-off-by: Gaël PORTAY <gael.portay+rtone@gmail.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

support/scripts/genimage.sh

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
+set -e
+
 die() {
   cat <<EOF >&2
 Error: $@