zdtm: create /run in a test root

iptables 1.6.2 fails without /run, because it tries to create
the /run/xtables.lock file

Test output: ================================
Fatal: can't open lock file /run/xtables.lock: No such file or directory
23:29:06.098:     4: ERR: netns-nf.c:21: Can't set input rule (errno = 2 (No such file or directory))
23:29:06.098:     3: ERR: test.c:315: Test exited unexpectedly with code 255
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

test/zdtm.py

@@ -155,7 +155,7 @@ class host_flavor:
 
 
 class ns_flavor:
-	__root_dirs = ["/bin", "/sbin", "/etc", "/lib", "/lib64", "/dev", "/dev/pts", "/dev/net", "/tmp", "/usr", "/proc"]
+	__root_dirs = ["/bin", "/sbin", "/etc", "/lib", "/lib64", "/dev", "/dev/pts", "/dev/net", "/tmp", "/usr", "/proc", "/run"]
 
 	def __init__(self, opts):
 		self.name = "ns"