Implementing Swap flag testing

[santicomp2014]

Swap flags should be tested for correctness.

A posible solution would be to use create a new test under config_test.go and spawn a new instance of swarm with the flags under test.

This is a reference implementation

The current approach does not work when swap is enable.

Fatal: Error starting protocol stack: connecting to Ethereum API, url bzzd.ipc: dial unix bzzd.ipc: connect: no such file or directory

A better approach should be found.