Automatic merge from submit-queue (batch tested with PRs 37094, 37663, 37442, 37808, 37826)

Node E2E: Fix node e2e firewall configure.

Get rid of the misleading error message:
```
W1129 12:57:16.967] E1129 12:57:16.967130   29815 remote.go:204] Failed to configured firewall: command [ssh -i /home/jenkins/.ssh/google_compute_engine -o UserKnownHostsFile=/dev/null -o IdentitiesOnly=yes -o CheckHostIP=no -o StrictHostKeyChecking=no -o ServerAliveInterval=30 -o LogLevel=ERROR 104.154.201.208 -- sudo sh -c 'iptables -L INPUT | grep "Chain INPUT (policy DROP)"&&(iptables -C INPUT -w -p TCP -j ACCEPT || iptables -A INPUT -w -p TCP -j ACCEPT)&&(iptables -C INPUT -w -p UDP -j ACCEPT || iptables -A INPUT -w -p UDP -j ACCEPT)&&(iptables -C INPUT -w -p ICMP -j ACCEPT || iptables -A INPUT -w -p ICMP -j ACCEPT)'] failed with error: exit status 1 output: 
W1129 12:57:17.271] E1129 12:57:17.271169   29815 remote.go:213] Failed to configured firewall: command [ssh -i /home/jenkins/.ssh/google_compute_engine -o UserKnownHostsFile=/dev/null -o IdentitiesOnly=yes -o CheckHostIP=no -o StrictHostKeyChecking=no -o ServerAliveInterval=30 -o LogLevel=ERROR 104.154.201.208 -- sudo sh -c 'iptables -L FORWARD | grep "Chain FORWARD (policy DROP)" > /dev/null&&(iptables -C FORWARD -w -p TCP -j ACCEPT || iptables -A FORWARD -w -p TCP -j ACCEPT)&&(iptables -C FORWARD -w -p UDP -j ACCEPT || iptables -A FORWARD -w -p UDP -j ACCEPT)&&(iptables -C FORWARD -w -p ICMP -j ACCEPT || iptables -A FORWARD -w -p ICMP -j ACCEPT)'] failed with error: exit status 1 output: 
W1129 12:57:17.557] E1129 12:57:17.556683   29815 remote.go:204] Failed to configured firewall: command [ssh -i /home/jenkins/.ssh/google_compute_engine -o UserKnownHostsFile=/dev/null -o IdentitiesOnly=yes -o CheckHostIP=no -o StrictHostKeyChecking=no -o ServerAliveInterval=30 -o LogLevel=ERROR 104.154.128.178 -- sudo sh -c 'iptables -L INPUT | grep "Chain INPUT (policy DROP)"&&(iptables -C INPUT -w -p TCP -j ACCEPT || iptables -A INPUT -w -p TCP -j ACCEPT)&&(iptables -C INPUT -w -p UDP -j ACCEPT || iptables -A INPUT -w -p UDP -j ACCEPT)&&(iptables -C INPUT -w -p ICMP -j ACCEPT || iptables -A INPUT -w -p ICMP -j ACCEPT)'] failed with error: exit status 1 output: 
W1129 12:57:17.771] I1129 12:57:17.771236   29815 remote.go:231] Killing any existing node processes on tmp-node-e2e-a1212c32-gci-dev-56-8977-0-0
W1129 12:57:17.877] E1129 12:57:17.877123   29815 remote.go:213] Failed to configured firewall: command [ssh -i /home/jenkins/.ssh/google_compute_engine -o UserKnownHostsFile=/dev/null -o IdentitiesOnly=yes -o CheckHostIP=no -o StrictHostKeyChecking=no -o ServerAliveInterval=30 -o LogLevel=ERROR 104.154.128.178 -- sudo sh -c 'iptables -L FORWARD | grep "Chain FORWARD (policy DROP)" > /dev/null&&(iptables -C FORWARD -w -p TCP -j ACCEPT || iptables -A FORWARD -w -p TCP -j ACCEPT)&&(iptables -C FORWARD -w -p UDP -j ACCEPT || iptables -A FORWARD -w -p UDP -j ACCEPT)&&(iptables -C FORWARD -w -p ICMP -j ACCEPT || iptables -A FORWARD -w -p ICMP -j ACCEPT)'] failed with error: exit status 1 output: 
W1129 12:57:17.898] I1129 12:57:17.898711   29815 remote.go:239] Extracting tar on tmp-node-e2e-a1212c32-gci-dev-56-8977-0-0
W1129 12:57:17.941] E1129 12:57:17.941566   29815 remote.go:204] Failed to configured firewall: command [ssh -i /home/jenkins/.ssh/google_compute_engine -o UserKnownHostsFile=/dev/null -o IdentitiesOnly=yes -o CheckHostIP=no -o StrictHostKeyChecking=no -o ServerAliveInterval=30 -o LogLevel=ERROR 104.154.154.237 -- sudo sh -c 'iptables -L INPUT | grep "Chain INPUT (policy DROP)"&&(iptables -C INPUT -w -p TCP -j ACCEPT || iptables -A INPUT -w -p TCP -j ACCEPT)&&(iptables -C INPUT -w -p UDP -j ACCEPT || iptables -A INPUT -w -p UDP -j ACCEPT)&&(iptables -C INPUT -w -p ICMP -j ACCEPT || iptables -A INPUT -w -p ICMP -j ACCEPT)'] failed with error: exit status 1 output: 
W1129 12:57:18.020] I1129 12:57:18.019802   29815 remote.go:231] Killing any existing node processes on tmp-node-e2e-a1212c32-coreos-alpha-1122-0-0-v20160727
W1129 12:57:18.024] E1129 12:57:18.024044   29815 remote.go:213] Failed to configured firewall: command [ssh -i /home/jenkins/.ssh/google_compute_engine -o UserKnownHostsFile=/dev/null -o IdentitiesOnly=yes -o CheckHostIP=no -o StrictHostKeyChecking=no -o ServerAliveInterval=30 -o LogLevel=ERROR 104.154.154.237 -- sudo sh -c 'iptables -L FORWARD | grep "Chain FORWARD (policy DROP)" > /dev/null&&(iptables -C FORWARD -w -p TCP -j ACCEPT || iptables -A FORWARD -w -p TCP -j ACCEPT)&&(iptables -C FORWARD -w -p UDP -j ACCEPT || iptables -A FORWARD -w -p UDP -j ACCEPT)&&(iptables -C FORWARD -w -p ICMP -j ACCEPT || iptables -A FORWARD -w -p ICMP -j ACCEPT)'] failed with error: exit status 1 output: 
```

The problem is that the command 'iptables -L FORWARD | grep "Chain FORWARD (policy DROP)" returns an error when the rule is not found, which is not expected behaviour.

@freehan