Fix some sched and tty tests

The ps sched test has been disabled. There are too many
odd build farms this fails in strange ways.

Other odd build farms have no tty and so some tests check
for no tty and skip if not found.

testsuite/pkill.test/pkill.exp

@@ -9,8 +9,7 @@ set not_uid [ expr { $uid + 1 } ]
 set gid [ exec id -g ]
 set not_gid [ expr { $gid + 1 } ] 
 set ps "${topdir}ps/pscommand"
-set raw_tty [ exec tty ]
-regexp "/dev/(.+)" $raw_tty > tty
+set tty [ get_tty ]
 
 set test "pkill with no arguments"
 spawn $pkill