scripts/prepare-release: option -k to specify the signing key

Make the GPG signing an optional argument. It doesn't make much sense to
require that when no assets are being generated (i.e. when "-b" is
used).

scripts/prepare-release.sh

@@ -5,19 +5,21 @@ this=`basename $0`
 
 usage () {
 cat << EOF
-Usage: $this [-h] [-a] [-b] RELEASE_VERSION GPG_KEY
+Usage: $this [-h] [-a] [-b] [-k GPG_KEY] RELEASE_VERSION
 
 Options:
   -h         show this help and exit
   -a         do not patch files in the repo
   -b         do not generate assets
+  -k         gpg key to use for signing the assets
 
 Example:
 
-  $this v0.1.2 "Jane Doe <[email protected]>"
+  $this v0.1.2 -k "Jane Doe <[email protected]>"
 
 
 NOTE: The GPG key should be associated with the signer's Github account.
+      Use -k to specify the correct key (if needed).
 EOF
 }
 
@@ -29,20 +31,22 @@ sign_helm_chart() {
   echo "$yaml
 ...
 files:
-  $chart: sha256:$sha256" | gpg -u "$key" --clearsign -o "$chart.prov"
+  $chart: sha256:$sha256" | gpg ${signing_key:+-u "$signing_key"} --clearsign -o "$chart.prov"
 }
 
 #
 # Parse command line
 #
 no_patching=
 no_assets=
-while getopts "abh" opt; do
+while getopts "abk:h" opt; do
     case $opt in
         a)  no_patching=y
             ;;
         b)  no_assets=y
             ;;
+        k) signing_key="$OPTARG"
+            ;;
         h)  usage
             exit 0
             ;;
@@ -54,8 +58,8 @@ done
 shift "$((OPTIND - 1))"
 
 # Check that no extra args were provided
-if [ $# -ne 2 ]; then
-    if [ $# -lt 2 ]; then
+if [ $# -ne 1 ]; then
+    if [ $# -lt 1 ]; then
         echo -e "ERROR: too few arguments\n"
     else
         echo -e "ERROR: unknown arguments: ${@:3}\n"
@@ -65,8 +69,7 @@ if [ $# -ne 2 ]; then
 fi
 
 release=$1
-key="$2"
-shift 2
+shift 1
 
 container_image=k8s.gcr.io/nfd/node-feature-discovery:$release