This commit breaks the large `testMultiHopHtlcClaims` into independent
test cases to take the advantage of parallel testing. The old setup will
put the stress of creating and syncing new blocks into a single core,
which causes a much longer test time and sometimes times out.
This commit changes how the context is created and inherited to better
reflex the relationship of the components. We now have the following
context structure,
```
For ephemeral nodes, the context chain is,
main HarnessTest -> sub HarnessTest -> HarnessNode -> HarnessRPC
For standby nodes, the context chain is,
main HarnessTest -> standby HarnessNode -> HarnessRPC
```
This commit adds a new struct, `HarnessNode`, to manage the lnd process
used in our itest. This struct is built upon `HarnessRPC`, `State`, and
`NodeWatcher`.
This commit adds a new struct, `nodeWatcher`, to keep track of all graph
topology updates of a given node, including updates from channel edges,
policies, and peers.
This commit adds a new package `lntemp/node` and inside it a new struct
`State` is added to track the internal node state. This enables us using
the same running nodes accross tests without wrong uncleaned states.
