scripts: Add extra check to hypervisor config script

Check the specified tag in `check_tag()` to ensure it is not blank
(which is invalid).

Signed-off-by: James O. D. Hunt <james.o.hunt@intel.com>

scripts/configure-hypervisor.sh

@@ -92,6 +92,8 @@ check_tag()
 	local tag="$1"
 	local entry="$2"
 
+	[ -z "$tag" ] && die "no tag for entry '$entry'"
+
 	value="${recognised_tags[$tag]}"
 
 	[ -n "$value" ] && return