dispvm: simplify DispVM preparation script

dispvm/qubes-prepare-saved-domain.sh

@@ -1,15 +1,15 @@
 #!/bin/bash
+
+set -o pipefail
+
 get_encoded_script()
 {
+	ENCODED_SCRIPT=`
 		if [ "$1" == "vm-default" ]; then
-        SCRIPT_CMD="echo /usr/lib/qubes/dispvm-prerun.sh"
-    elif ! [ -f "$1" ] ; then
-		echo $1 is not a file ?
-		exit 1
+			echo /usr/lib/qubes/dispvm-prerun.sh
 		else
-        SCRIPT_CMD="cat $1"
-	fi	
-	ENCODED_SCRIPT=`$SCRIPT_CMD | perl -e 'use MIME::Base64 qw(encode_base64); local($/) = undef;print encode_base64(<STDIN>)'|tr -d "\n"`
+			cat "$1"
+		fi | base64 -w0` || exit 1
 }
 
 if [ $# != 2 -a $# != 3 ] ; then