lnd: support space characters surrounding = in bitcoind configuration files
lnd: support space characters surrounding = in bitcoind configuration files

lnd can't detect bitcoind configuration if the config file has spaces around the = character, e.g.:
```
zmqpubrawblock = tcp://127.0.0.1:28332
zmqpubrawtx = tcp://127.0.0.1:28332
rpcuser = rpcuser
```
I had to dig into the source code to understand what was wrong.

This patch solves this problem, bitcoind's config parsing source code can be seen at https://github.com/bitcoin/bitcoin/blob/master/src/util.cpp
LightningNetwork/lnd,aakselrod/lnd,LightningNetwork/lnd,aakselrod/lnd