Allow configuration of logrorate in GCE

cluster/common.sh

@@ -759,7 +759,9 @@ EOF
 
     for var_name in ${PROVIDER_VARS}; do
       eval "local var_value=\$(yaml-quote \${${var_name}})"
-      echo "${var_name}: ${var_value}" >>$file
+      cat >>$file <<EOF
+${var_name}: ${var_value}
+EOF
     done
   fi