speed up strongswan setup

I think repeating 30s each time strongswan test runs is not necessary. It's running 5 times. One setup and one teardown makes the trick.

Feature: nmcli: strongswan
Executing @strongswan
* waiting for testeth0 to connect
 ** we do have IPv4 complete
  @strongswan ... passed in 30.096s
NetworkManager process id before: 401453
before_scenario ... passed in 30.752s