lotus-shed: add consensus check command

[travisperson]

Consensus check verifies that all nodes share a common tipset for a given height.

The height flag specifies a chain height to start a comparison from. There are two special arguments for this flag. All other expected values should be chain tipset heights.
@common - Use the maximum common chain height between all nodes
@expected - Use the current time and the genesis timestamp to determine a height

Examples

Find the highest common tipset and look back 10 tipsets

lotus-shed consensus check --height @common --lookback 10

Calculate the expected tipset height and look back 10 tipsets

lotus-shed consensus check --height @expected --lookback 10

Check if nodes all share a common genesis

lotus-shed consensus check --height 0

Check that all nodes agree upon the tipset for 1day post genesis

lotus-shed consensus check --height 2880 --lookback 0

[magik6k]

Noice