fix(core-blockchain): discard blocks containing forged tx and stop process queue on fork

[spkjp]

Proposed changes

This PR fixes and refactors some issues with block processing and download in general.

• Move block exception check to the beginning of processBlock
• When downloading blocks, it can cause a fork at any time. The process queue is not paused immediately and may push one more block for the current round => revertRound hits an assert

See that there's 920,758 after the FORK event:

[2018-12-14 20:20:19][INFO]    : Downloaded 139 new blocks accounting for a total of 1 transaction
[2018-12-14 20:20:19][WARN]    : Downloaded block not accepted: {"id":"15050679645209862619","version":0,"timestamp":54709946,"height":920767,"reward":"200000000","previousBlock":"2018383776580683639","numberOfTransactions":0,"totalAmount":"0","totalFee":"0","payloadLength":0,"payloadHash":"e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855","generatorPublicKey":"03d3c6889608074b44155ad2e6577c3368e27e6e129c457418eb3e5ed029544e8d","blockSignature":"30450221008ec05d4bb0d3f5fbe00871736f371173448c4de4f9008e160d6094c2a90320b802206b1072972a46544bcec7f1860b71c03f29f9579942dba7ee6fc132def815554d","ip":"95.179.235.167"}
[2018-12-14 20:20:19][WARN]    : Last block: {"id":"3306179701556476362","version":0,"timestamp":54713664,"height":920766,"reward":"200000000","previousBlock":"16386574835420196172","numberOfTransactions":0,"totalAmount":"0","totalFee":"0","payloadLength":0,"payloadHash":"e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855","generatorPublicKey":"029a20963b506afabb2bd805830a46cef8d59218cd88c0dca9d2a0158045b1c3e0","blockSignature":"3045022100ee2f3cdee81733064b17221abfaa964ac2d62dc3bb7a8fa39f146746b25e3d2a02206e7d4f3967cc570709af74e8d08162b2fd565b8cc057571c5d53f8c5d74cfd2d","ip":"167.114.43.52"}
[2018-12-14 20:20:19][DEBUG]   : event 'FORK': {"syncWithNetwork":"downloadBlocks"} -> {"fork":"analysing"} -> actions: [startForkRecovery, analyseFork]
[2018-12-14 20:20:19][DEBUG]   : Delegate xillion (02d2a18dcb0dd7abd0a91ca70cb79d04e1ff7a4e77d1d8beda3d6c0a51b55a5db1) allowed to forge block 920,758 👍
...
[2018-12-14 20:20:20][INFO]    : Undoing block 920,757
(node:31146) UnhandledPromiseRejectionWarning: AssertionError [ERR_ASSERTION]: The expression evaluated to a falsy value:  assert_1.default(this.blocksInCurrentRound.pop().data.id === block.data.id)

This is fixed by ensuring the process queue is stopped first when starting a fork recovery.

Furthermore:

• When a chained block is received, it is dropped if it contains a forged transaction. (hurts a bit)
• After database recovery, the blocksInCurrentRound were not updated which caused the same assert failure as above.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (improve a current implementation without adding a new feature or fixing a bug)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Build (changes that affect the build system)
• Docs (documentation only changes)
• Test (adding missing tests or fixing existing tests)
• Other... Please describe:

Checklist

• I have read the CONTRIBUTING documentation
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[codecov-io]

Codecov Report

Merging #1732 into develop will increase coverage by <.01%.
The diff coverage is 38.59%.

@@            Coverage Diff             @@
##           develop   #1732      +/-   ##
==========================================
+ Coverage     39.9%   39.9%   +<.01%     
==========================================
  Files          352     352              
  Lines         7665    7685      +20     
  Branches      1100    1091       -9     
==========================================
+ Hits          3059    3067       +8     
- Misses        4590    4604      +14     
+ Partials        16      14       -2

Impacted Files	Coverage Δ
packages/core-blockchain/src/state-storage.ts	85.71% <ø> (-0.21%)	⬇️
packages/core-p2p/src/court/guard.ts	0% <0%> (ø)	⬆️
packages/core-p2p/src/monitor.ts	0% <0%> (ø)	⬆️
packages/core-blockchain/src/state-machine.ts	42.92% <37.5%> (-0.89%)	⬇️
packages/core-database/src/interface.ts	28.98% <50%> (+0.72%)	⬆️
packages/core-blockchain/src/blockchain.ts	69.23% <51.72%> (-1.74%)	⬇️
packages/core-deployer/src/utils.ts	0% <0%> (ø)	⬆️
packages/core-logger-winston/src/formatter.ts	0% <0%> (ø)	⬆️

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