zdtm: fifo-rowo-pair test update

Address Andrew's comments

 - use TEST_VALUE macro instead of open coded value
 - use WIFx macros for child status testing
 - kill child/parent on error

Note that it was not clear from an initiall patch
change log -- the difference between fifo_wronly
test case and this one is that we use fork() call
here which allow us to make sure that fifo restoration
code logic will be tested more widely.

Basically the flowchart of the test case:

parent				child
------				-----
open RW fifo (slave)
open RO fifo (master)
				open WO fifo (master)
				dup parent slave to slave1

				... waiting c/r to happen ...
				... waking up from c/r ...

				send bytes to master
				send bytes to slave1

				finish
... initiating c/r ...
... waking up from c/r ...

read bytes from master
read bytes from slave

PASS :D

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>