Replacing "sleep 365d" with "sleep inf"

To get endless sleep, `sleep inf` (or `sleep infinity`) can be used
instead of `sleep 365d`. Coreutils' sleep accepts any floating-point
number as an argument, which may be 'infinity', according to
`man strtod`.

qubes-rpc/qubes.WaitForSession

@@ -1,2 +1,2 @@
 read USERNAME
-su -c 'echo $$ >> /tmp/qubes-session-waiter; [ ! -f /tmp/qubes-session-env ] && exec sleep 365d' - "$USERNAME" 2> /dev/null
+su -c 'echo $$ >> /tmp/qubes-session-waiter; [ ! -f /tmp/qubes-session-env ] && exec sleep inf' - "$USERNAME" 2> /dev/null