[Experimental] ci test: sync w bitcoin core

[pinheadmz]

I'm currently working on #721 which requires upgrades to the on-the-wire protocol, and I need to make sure I stay in sync (and not get banned) from bitcoind nodes.

This PR is an attempt to integrate bitcoind compatibility into our CI pull-testing.

I made a series of scripts that connect any number of bcoin and bitcoind nodes and uses RPC commands to test headers-first sync (work-in-progress): https://github.com/pinheadmz/networktest. I copied one of those tests into this PR, which syncs bcoin and bitcoind, then triggers a reorg from bitcoind by invalidating a block and building a new chain from there. For now, I've left on all the logging output and you can see its output in the testing report.

For local testing, a new command is added to package.json. For CI testing, the config.yaml has been updated to actually install bitcoind, and run an extra set of tests that connect it to bcoin.

To test the CircleCI changes locally, you can install the circleCI CLI tool and run the command:
circleci local execute --job install
Unfortunately the local CI tool doesn't manage workflows like the online CI tester, so one command must be uncommented to work locally. (see the comments in .circleci/config.yml )

Testing API changes

Not Affected

npm run test
npm run test-file

Added

npm run bitcoind-test
(only runs tests in /test/bitcoind-sync/*-test.js which require bitcoind to be installed and available as a command)

Modified

npm run test-ci
(adds all files in /test/bitcoind-sync/*-test.js to "test" job, included in codecov)

[codecov-io]

Codecov Report

Merging #759 into master will increase coverage by 5.1%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master     #759     +/-   ##
=========================================
+ Coverage   56.64%   61.74%   +5.1%     
=========================================
  Files         112      112             
  Lines       28140    28140             
  Branches     4800     4800             
=========================================
+ Hits        15939    17376   +1437     
+ Misses      12201    10764   -1437

Impacted Files	Coverage Δ
lib/mempool/fees.js	52.5% <0%> (-8.84%)	⬇️
lib/script/script.js	78.36% <0%> (+0.42%)	⬆️
lib/node/http.js	48.49% <0%> (+0.5%)	⬆️
lib/script/opcode.js	78.59% <0%> (+0.66%)	⬆️
lib/net/bip152.js	78.38% <0%> (+0.86%)	⬆️
lib/blockstore/file.js	99.56% <0%> (+0.87%)	⬆️
lib/blockchain/chaindb.js	58.51% <0%> (+1.3%)	⬆️
lib/node/rpc.js	27.71% <0%> (+1.45%)	⬆️
lib/node/fullnode.js	60.24% <0%> (+2.4%)	⬆️
lib/node/node.js	69.18% <0%> (+4.06%)	⬆️
... and 12 more

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[braydonf]

This is similar to https://cdecker.github.io/lightning-integration/ and could include btcd as well.