Fix address encoding in rpc_client:deploy_solidity_contract
Fix address encoding in rpc_client:deploy_solidity_contract

At least since https://github.com/ethereum/go-ethereum/pull/3355 (v1.5.4) geth
enforces proper hex encoding (with leading `0x`) for addresses. This makes the
current rpc_client behavior of pyethapp incompatible, since the polling code
for deployment was using the `0x`-stripped contract address.

ethereum/pyethapp,changwu-tw/pyethapp,gsalgado/pyethapp,changwu-tw/pyethapp,gsalgado/pyethapp,ethereum/pyethapp