Allow the user to specify server names

[anthonydahanne]

In galvan, server names are generated with the following pattern :

      String serverName = "testServer" + (i + serverStartNumber);

I would like to write a galvan test using my own server names (to assert whether or not other parts of the system work fine with server names with special characters), but I can't.

cc @mathieucarbou to simulate a server with a name like "10.0.1.1:9510"

[mathieucarbou]

@anthonydahanne it will be also useful when simulating same server names

[anthonydahanne]

@mathieucarbou true !