macos installer: Default to using ad-hoc signing

When there is no signing identity to pass to the macOS `codesign` tool,
we can use `-` instead as the identity to perform ad-hoc signing.

From `man codesign`:
> If identity is the single letter "-" (dash), ad-hoc signing is
> performed.  Ad-hoc signing does not use an identity at all

This makes it easier to test the sign() code-path in package.sh as
we'll run the same code regardless of `NO_CODESIGN` being set or not.

Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>

contrib/pkginstaller/package.sh

@@ -4,7 +4,7 @@ set -euxo pipefail
 
 BASEDIR=$(dirname "$0")
 OUTPUT=$1
-CODESIGN_IDENTITY=${CODESIGN_IDENTITY:-mock}
+CODESIGN_IDENTITY=${CODESIGN_IDENTITY:--}
 PRODUCTSIGN_IDENTITY=${PRODUCTSIGN_IDENTITY:-mock}
 NO_CODESIGN=${NO_CODESIGN:-0}
 HELPER_BINARIES_DIR="/opt/podman/bin"
@@ -25,9 +25,6 @@ function build_podman() {
 }
 
 function sign() {
-  if [ "${NO_CODESIGN}" -eq "1" ]; then
-    return
-  fi
   local opts=""
   entitlements="${BASEDIR}/$(basename "$1").entitlements"
   if [ -f "${entitlements}" ]; then