Export die() function

I realised I'd been using die() in a few places assuming it was
available, but it wasn't exported.  I guess it didn't matter because
whatever was wrong, we were failing anyway :)

This exports the function to make it available to sub-processes, which
should remove the need to source it as done in several places.

Change-Id: I7b9a5a6db406e160099b6ed9fde80455ae227327

elements/base/extra-data.d/50-store-build-settings

@@ -7,7 +7,6 @@ fi
 set -eu
 set -o pipefail
 
-source $_LIB/die
 [ -n "$TMP_HOOKS_PATH" ] || die "Temp hook path not set"
 
 echo "$DIB_ENV" > $TMP_HOOKS_PATH/dib_environment

elements/local-config/extra-data.d/62-ssh-key

@@ -8,7 +8,6 @@ fi
 set -eu
 set -o pipefail
 
-source $_LIB/die
 [ -n "$TMP_HOOKS_PATH" ] || die "Temp hook path not set"
 
 if [ -e ~/.ssh/authorized_keys ]; then

elements/partitioning-sfdisk/block-device.d/10-partitioning-sfdisk

@@ -7,7 +7,6 @@ set -eu
 set -o pipefail
 
 # sanity checks
-source $_LIB/die
 [ -n "$IMAGE_BLOCK_DEVICE" ] || die "Image block device not set"
 
 # execute sfdisk with the given partitioning schema

elements/vm/block-device.d/10-partition

@@ -6,7 +6,6 @@ fi
 set -eu
 set -o pipefail
 
-source $_LIB/die
 [ -n "$IMAGE_BLOCK_DEVICE" ] || die "Image block device not set"
 
 # Create 2 partitions for PPC, one for PReP boot and other for root

lib/die

@@ -16,10 +16,11 @@
 
 # Prints "message" and exits
 # Usage: die "message"
-function die() {
+function die {
     local exitcode=$?
     set +o xtrace
     echo $@
     exit $exitcode
 }
 
+export -f die