zdtm: remove error messages, that this directory is exist

Like this:
mkdir: cannot create directory ‘/tmp/criu-root.wt2oW0/lib64’: File exists
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm.sh

@@ -218,10 +218,10 @@ construct_root()
 	local libdir=$root/lib
 	local libdir2=$root/lib64
 
-	mkdir $root/bin
+	mkdir -p $root/bin
 	cp $ps_path $root/bin
 
-	mkdir $libdir $libdir2
+	mkdir -p $libdir $libdir2
 	for i in `ldd $test_path $ps_path | grep -P '^\s' | awk '{ print $1 }' | grep -v vdso`; do
 		local lib=`basename $i`
 		[ -f $libdir/$lib ] && continue ||