pipeio/pipeio.c: cleanup and add it to run default

Delete some useless comments and fix some.

Use SAFE_* macros.

Make a re-arrangement on original code: let parent process
work in do_parent(), child process work in do_child(), and
arguments parse and initialization work in setup().

Delete several useless or pointless options:
  Option C: this option is not supported and has no effect to this test.

  Option B: if this option is specified, the parent process will always
return 0, which won't reflect the correct test results. I think it does
not make much sense and remove it.

  Option d: this option is used to specify a directory, where named pipe
is created, other than the current directory. Since tst_tmpdir() will
create a temporary directory, so I think "-d" option can be removed.

printf() is not async-signal-safe, so use write(2) in signal handler directly.

Some cleanup.

Signed-off-by: Xiaoguang Wang <wangxg.fnst@cn.fujitsu.com>
Acked-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>