tests/sched.test: use heredoc in order to avoid spawning of subprocess

tests/sched.test: use heredoc in order to avoid spawning of subprocess

Pipelined commands executed in subprocesses (some shells have special
provision for last command in the pipeline, but it is not guaranteed
and not POSIX), so exit codes of these subprocesses can be lost.
In order to avoid creating subprocesses, input for read commands
is better to supply via heredoc and not pipe.

* tests/sched.test: Move test cases to heredoc.