fsstress-gocryptfs.bash: don't hang if TMPDIR ends in /

We would hang like this

   ./fsstress-loopback.bash
  Recompile go-fuse loopback: v2.0.3-7-g0b6cbc5
  Waiting for mount: xxxxxxxx^C

if TMPDIR has a trailing /. The reason is that the
paths in /proc/self/mounts are normalized, while
TMPDIR may not be.

tests/stress_tests/fsstress-gocryptfs.bash

@@ -70,7 +70,7 @@ fi
 
 sleep 0.5
 echo -n "Waiting for mount: "
-while ! grep "$MNT fuse" /proc/self/mounts > /dev/null
+while ! grep "$(basename $MNT) fuse" /proc/self/mounts > /dev/null
 do
 	sleep 1
 	echo -n x