scripts: never exit 1, always call err instead

this same change has been applied, selectively, to
certain return statements. the general rule is this:
the return statement should only be used to direct
logic within a script, where certain non-errors
states are used to skip certain actions; the exit
command should *never* be used to return non-zero,
except by err(). in so doing, we ensure easier
debugging of the build system

also: strip_rom_image in build/release/roms was
running "continue" when a rom file didn't exist,
despite not being a while/for loop. i make it
return (non-error condition) instead

it's ok for a script to exit 0, where appropriate,
but perhaps a function could also be written for it

Signed-off-by: Leah Rowe <leah@libreboot.org>

resources/scripts/build/coreboot/utils

@@ -27,12 +27,14 @@ main()
 {
 	if [ $# -gt 0 ]; then
 		for board in "${@}"; do
-			build_for_mainboard ${board} || exit 1
+			build_for_mainboard ${board} || \
+			    err "cannot build cbutils for target, ${board}"
 		done
 	else
 		for boarddir in resources/coreboot/*; do
 			[ ! -d "${boarddir}" ] && continue
-			build_for_mainboard ${boarddir##*/} || exit 1
+			build_for_mainboard ${boarddir##*/} || \
+			    err "cannot build cbutils for target, ${board}"
 		done
 	fi
 }