functional-tester: latency Injection shows error on live tester

[fanminshi]

The current 3 node tester is reporting error on latency injection.

2016-11-09 18:18:23.568204 I | etcd-agent: set latency of 500ms (+/- 50ms)
2016-11-09 18:18:23.648393 I | etcd-agent: error setting latency exit status 1
2016-11-09 18:18:23.784513 I | etcd-agent: removing latency
2016-11-09 18:18:23.802817 I | etcd-agent: error removing latency

The current tester inject latency on dev eth0(https://github.com/coreos/etcd/blob/master/pkg/netutil/isolate_linux.go#L49), but the agents don't have dev eh0

fanminshi@test01-agent01:~$ ifconfig
ens4      Link encap:Ethernet  HWaddr 42:01:0a:f0:00:02
          inet addr:10.240.0.2  Bcast:10.240.0.2  Mask:255.255.255.255
          inet6 addr: fe80::4001:aff:fef0:2/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1460  Metric:1
          RX packets:508807089 errors:0 dropped:0 overruns:0 frame:0
          TX packets:625083325 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:596458454684 (596.4 GB)  TX bytes:473036079782 (473.0 GB)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:525075 errors:0 dropped:0 overruns:0 frame:0
          TX packets:525075 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1
          RX bytes:30065638 (30.0 MB)  TX bytes:30065638 (30.0 MB)

we need a programmatic way to configure network interface.

[xiang90]

@fanminshi For these env dependent tests, probably we can just skip it if failure injection fails?

[fanminshi]

@xiang90 the current tester will skip if latency injection has failed. So the tester still proceed. the problem is that latency injection failure is not being tested at all on live tester.

[xiang90]

@fanminshi OK. That is bad. We should fix it.

[fanminshi]

Yeah, I noticed this problem when I am working on #5614.