Change Description

When the flag stopatheight is set to something greater than zero, btcd stops immediately after processing the height provided.

Also, we won't let the node start if the current height is equal or greater than the provided stopatheight.

This is a very useful feature for testing purposes.

Steps to Test

To test that the node is stopping at the expected height, execute btcd with the flag --stopatheight=N, the node should stop after processing the block N, it can be verified by starting the node with --connect=127.0.0.1:invalid_port and without the --stopatheight flag, the log will show that the chainstate is at height N.

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