tests: don't ever leave a backgrounded "sleep 10m" process

* tests/misc/help-version: Sleep only ~30s, not 10m.
The latter was a problem when somehow that sleep process would
hang around and thereby prevent (for up to 10m) a normal unmount
of the temporary partition in which I'd run the tests.

tests/misc/help-version

@@ -226,7 +226,7 @@ id_setup () { args=-u; }
 
 # Use env to avoid invoking built-in sleep of Solaris 11's /bin/sh.
 kill_setup () {
-  env sleep 10m &
+  env sleep 31.5 &
   args=$!
 }