zdtm.sh: set correct path for dump files (v3)

Don't use an uninitialized variable to create a path pattern.

v2: fix the comment
v3: don't use readlink -m, which isn't supported by busybox

Cc: Christopher Covington <cov@codeaurora.org>
Reported-by: Christopher Covington <cov@codeaurora.org>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Reviewed-by: Christopher Covington <cov@codeaurora.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm.sh

@@ -661,7 +661,8 @@ EOF
 		gen_args="$gen_args --force-irmap"
 	fi
 
-	ddump=`readlink -fm dump/$test_name/$PID/$i`
+	# X will be substituted with an iteration number
+	ddump=`pwd`/dump/$test_name/$PID/X
 	for i in `seq $ITERATIONS`; do
 		local cpt_args=
 		local dump_only=