Fixes#457.
The SignOutputRaw RPC is normally too lenient when it comes to fields
not being set, which is why this used to work previously. But with lnd
in remote signing mode, we need all the extra meta information available
on an input being signed for, so we actually need the pk script being
set.
Loop fully works with a remote signing lnd backend pair after applying
this fix.
We need the newer version of lndclient to get our synced to chain
state. This requires changes to our test mock, so it is separated
into a different commit. Since lndclient is expanding to be used in
projects other than loop, the client interface is embedded in our
mock rather than implementing functions we do not need. Functions that
we already use in tests are updated accordingly.
Note that while this commit bumps us to a version of lndclient that
defaults to requiring lnd 0.11, we do not bump our required version
yet because we are not using any new endpoints.