Gas estimation is unreliable in release v1.5.3 with espresso enabled

[piersy]

Description

Gas estimation is unreliable in release v1.5.3 with espresso enabled.

Calling estimate gas on a non validating node can sometimes return a gas estimate that is too low. When run against alfajores these tests are often failing due to the gas estimates being too low. This only seems to happen when calling estimate gas on non validating nodes and is a problem that manifests with the Espresso hard fork.

The specific case where the gas estimate seems to be too low is when a contract transaction is estimated against a pending block that contains the contract deployment. In such cases the estimation comes out slightly low.

This issue is exacerbated by another problem which is that the pending block is not updated in a timely fashion. Pending blocks should represent the next block to insert, but currently the pending block is update is delayed by the length of time of a block, so that the pending block for the most part shares the same number as the most recently inserted block.