Fix rpc gas strategy

[fselmo]

What was wrong?

• rpc_gas_price_strategy incorrectly returns the hex value without convesion to int even though the defined return type is Wei.
• We don't have tests to catch this
• bonus: Let's also not assume the value will always be an int and only convert to hex if it is an int in the gas_price_strategy_middleware.

How was it fixed?

• In the rpc_gas_price_strategy, use the eth module gas_price call which always returns an int, rather than request_blocking which can be variable depending on the provider.
• Convert gasPrice value from strategy to hex only if it's an int
• Add tests that would've failed before this change. The reason here is we only test on EthereumTesterProvider (core test suite)... but eth-tester already returns an int, even though most providers return the hex value.

Todo:

• Add entry to the release notes

Cute Animal Picture

[kclowes]

LGTM! 🚀