Read link to canonical path of GUID file

By default, it resolves the link path literally, which causes problem if
other commands do not run on the same directory the link is at.

For: QubesOS/qubes-core-admin#757
For: QubesOS/qubes-notification-proxy#13
For: QubesOS/qubes-issues#9940
For: QubesOS/qubes-issues#1512

Author: ben-grande

qubes-rpc-dom0/qubes.WaitForSession

@@ -16,7 +16,7 @@ if ! [ -L "$qrexec_name_sock" ]; then
     exit 1
 fi
 
-qrexec_id_sock=$(readlink "$qrexec_name_sock")
+qrexec_id_sock=$(readlink -e "$qrexec_name_sock")
 
 if [ -z "$qrexec_id_sock" ]; then
     echo "$0: readlink failed for $qrexec_name_sock" >&2