Generate pre-funded accounts in Polkadot format

[bernardoaraujor]

Currently, the funder module generates pre-funded addresses in generic Substrate format (5...).

As soon as

polkadot-stps/tests/relay.json

Line 8 in 5ec907c

"chain": "rococo-local",

is switched to polkadot-dev, the setup breaks with:

thread 'main' panicked at 'Account has insufficient funds', src/pre/mod.rs:49:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
rust process exited with code 101
...
Error: Rpc(Request("{\"jsonrpc\":\"2.0\",\"error\":{\"code\":1010,\"message\":\"Invalid Transaction\",\"data\":\"Inability to pay some fees (e.g. account balance too low)\"},\"id\":4}"))
rust process exited with code 1

In order to fulfil #15, the funder module needs to be adapted so it generates addresses in Polkadot format (1...).