We may close the master before reading the slave if the child runs first
when the parent wakes it up using task_waiter_complete. In this case the
subsequent read from the slave will return 0 resulting in a false
positive test failure:

13:23:42.194: 30914: ERR: pty02.c:89: read(slave) failed (errno = 11 (Resource temporarily unavailable))

Fix this by waking the child, which closes the master, only after the
read has been completed.

Also note errno = EAGAIN in the failure report above, which looks really
confusing. Let's print the actual number of bytes read/written along
with the errno while reporting a read/write failure to make the error
reporting clearer in this test.
Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>
Cc: Cyrill Gorcunov <gorcunov@parallels.com>
Acked-by: Andrew Vagin <avagin@parallels.com>
Acked-by: Cyrill Gorcunov <gorcunov@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>