Be able to use other network device in iptables

In `net/iptables`, it uses the network device `eth0` for network
operations. But the network device may be different on some machines. So
create a function to accept a network device parameter.

jepsen/src/jepsen/net.clj

@@ -172,8 +172,9 @@
     (fast!  [net test])
     (shape! [net test nodes behavior])))
 
-(def iptables
-  "Default iptables (assumes we control everything)."
+(defn iptables-with-dev
+  "Default iptables (assumes we control everything). Take network device as parameter."
+  [dev]
   (reify Net
     (drop! [net test src dest]
       (on-nodes test [dest]
@@ -185,32 +186,33 @@
       (with-test-nodes test
         (su
           (exec :iptables :-F :-w)
-          (exec :iptables :-X :-w))))
+          ; (exec :iptables :-X :-w)
+          )))
 
     (slow! [net test]
       (with-test-nodes test
-        (su (exec tc :qdisc :add :dev :eth0 :root :netem :delay :50ms
+        (su (exec tc :qdisc :add :dev dev :root :netem :delay :50ms
                   :10ms :distribution :normal))))
 
     (slow! [net test {:keys [mean variance distribution]
                       :or   {mean         50
                              variance     10
                              distribution :normal}}]
       (with-test-nodes test
-        (su (exec tc :qdisc :add :dev :eth0 :root :netem :delay
+        (su (exec tc :qdisc :add :dev dev :root :netem :delay
                   (str mean "ms")
                   (str variance "ms")
                   :distribution distribution))))
 
     (flaky! [net test]
       (with-test-nodes test
-        (su (exec tc :qdisc :add :dev :eth0 :root :netem :loss "20%"
+        (su (exec tc :qdisc :add :dev dev :root :netem :loss "20%"
                   "75%"))))
 
     (fast! [net test]
       (with-test-nodes test
         (try
-          (su (exec tc :qdisc :del :dev :eth0 :root))
+          (su (exec tc :qdisc :del :dev dev :root))
           (catch RuntimeException e
             (if (re-find #"Error: Cannot delete qdisc with handle of zero."
                          (.getMessage e))
@@ -232,6 +234,10 @@
                                    (str/join ","))
                               :-j :DROP :-w))))))))
 
+(def iptables
+  "Default iptables. Use eth0 as network device."
+  (iptables-with-dev :eth0))
+
 (def ipfilter
   "IPFilter rules"
   (reify Net