feat: external mode of lnd

[reliveyy]

This PR adds "external" mode for lndbtc and lndltc. It's a prerequisite of https://github.com/ExchangeUnion/raspiblitz/tree/xud

How to test?

bash xud.sh --lndbtc.mode=external --lndbtc.rpc-host=127.0.0.1 --lndbtc.rpc-port=10009 \
--lndbtc.certpath=~/.lnd/tls.cert \
--lndbtc.macaroonpath=~/.lnd/data/chain/bitcoin/mainnet/admin.macaroon

[raladev]

• does not work at all - instead of using external lnd, utils starts own lnd with neutrino mode.
  So, it seems that --bitcoind/litecoind.mode=neutrino that is used by default is more important then --lndltc.mode=external.

bash xud.sh external-lnd --lndltc.mode=external --lndltc.rpc-host=127.0.0.1 --lndltc.rpc-port=31009 --lndbtc.certpath=~/.xud-docker/simnet/data/lndbtc/tls.cert --lndbtc.macaroonpath=/home/native/.xud-docker/simnet/data/lndbtc/data/chain/bitcoin/simnet/admin.macaroon

Screenshot from 2020-10-13 16-52-35
Screenshot from 2020-10-13 16-52-23

[raladev]

Above

[raladev]

• utils stuck on Warming up step

Steps:

1. external lndltc is initialized and worked
2. testnet folder is clean
3. bash xud.sh -b external-lnd --lndltc.mode=external --lndltc.rpc-host=127.0.0.1 --lndltc.rpc-port=31009 --lndltc.certpath=~/.xud-docker/simnet/data/lndltc/tls.cert --lndltc.macaroonpath=/home/native/.xud-docker/simnet/data/lndltc/data/chain/litecoin/simnet/admin.macaroon

Actual result:

Screenshot from 2020-10-15 16-00-57
Screenshot from 2020-10-15 16-00-55

testnet.log

Looks like initialization step is skipped and utils tries to get access to xud (see testnet.log)

Expected result:

1. lndbtc neutrino sync
2. wallet initialization for lndbtc and xud
3. xud unlock

[raladev]

• host can not be None (xud exception)
  Screenshot from 2020-10-16 16-43-51
  Screenshot from 2020-10-16 16-43-44