estimateGas returns "contract address collision" error

[yihuang]

System info: ethermint main

Steps to reproduce:

$ seth send --create `jq -r '.bytecode' integration_tests/contracts/artifacts/contracts/TestMessageCall.sol/TestMessageCall.json` --gas 212958
...success deployed
$ seth estimate --create `jq -r '.bytecode' integration_tests/contracts/artifacts/contracts/TestMessageCall.sol/TestMessageCall.json` "0x"
seth-rpc: error:   code       -32000
seth-rpc: error:   message    rpc error: code = Unknown desc = rpc error: code = Internal desc = contract address collision: unknown request

Expected behavior: estimateGas should work in such case.

Actual behavior: [What actually happened]

Additional info:

In this PR: #851, we changed the state transition logic to use tx.nonce, but with estimateGas, the nonce in request could be zero, which cause "contract address collision" in evm.