zdtm.sh: fixed shared libraries retrieval

The pipe retrieving shared libraries the test depends on

ldd $test_path $ps_path | awk '/^\s/{ print $1 }'

doesn't actually produce any output so all NS tests fail
bacause the system linker fails to locate shared libraries
the test program depends on. This patch fixes the pipe
to retrieve the list of libraries properly.

Signed-off-by: Alexander Kartashov <alekskartashov@parallels.com>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>