For the purposes of better supporting new EIP prototyping and testing, we'd like to support activating EIPs without including them into any fork. This way we'll be able to run the consesus rules that include the new EIP before it is accepted into the next fork.

As a first step we'd like to support test generation of State Tests in testeth with any non-finalized EIP on top of the last hard fork.

So where regular test fillers have network name in the expect section like

        "expect" : [
            {
                "indexes" : { "data" : -1, "gas" : -1, "value" : -1 },
                "network" : [ "Istanbul"],
                 ...

the new format should support <forkName+EIPnumber> e.g.

        "expect" : [
            {
                "indexes" : { "data" : -1, "gas" : -1, "value" : -1 },
                "network" : [ "Istanbul+2046"],
                 ...

This could also include several EIP numbers, delimited by +.

cc @winsvega