Test that pluto does not crash when logical interface is removed

 * east <=> 192.1.2.23 <=> 192.1.3.1 (eth3)
 * west <=> 192.1.2.45 <=> 192.1.3.2 (eth3)
 
 1) east creates 192.1.3.1 eth3 tunnel to west
 2) west creates 192.1.3.2 eth3 tunnel to east
 3) west adds an iptable rule to block plaintext from eastnet
 4) west pings 192.0.2.254, but pong should be dropped by rule
 5) west 192.1.3.2 (eth3) initiates "test1" connection; east 192.1.3.1 (eth3) responds
 6) west confirms with ping
 7) west adds 192.1.3.3 to eth3 and reloads
 8) west 192.1.3.3 (eth3) initiates "test2" connection; east 192.1.3.1 (eth3) responds
 9) west initiates connection "westnet-eastnet"; east 192.1.2.23 responds
10) west confirms with ping
11) west removes 192.1.3.3 from eth3
12) east adds 192.1.3.3 to eth3
13) both east and west reload and confirm that pluto does not crash
