In this commit, we introduce two mining methods, `MineBlocks` and
`MineBlocksAndAssertNumTxes`, to `HarnessTest`. These methods are
different from the miner's methods as they would 1) mine the blocks
slowly and 2) assert all active nodes have synced. The miner's methods
are kept for future tests such as mining blocks really fast and see the
behavior of `lnd`.
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 replaces the keys used in the maps `activeNodes` and
`standbyNodes` from `pubkeyStr` to `NodeID` such that even the node is
not properly started, we can still clean it up during shutdown.
This commit adds a new component, `HarnessTest`, as a test manager, which
is responsible for managing the state change in the itest. It is built
on top of `HarnessNode` and will be handling assertions so that a test
can be created without unnecessary attention to node's unwanted
failures. This commit also adds a minimal set of assertions.
