This commit was previously split into the following parts to ease
review:
- 2d746f68: replace imports
- 4008f0fd: use ecdsa.Signature
- 849e33d1: remove btcec.S256()
- b8f6ebbd: use v2 library correctly
- fa80bca9: bump go modules
This commit removes the context as a param needed when calling methods
of HarnessNode. This change moves the context management inside
HarnessNode, aside from saving us a few lines, it makes the context
creation/timeout less error-prone.
This commit refactored the function NewNode to take a *testing.T so that
the unexpected error is checked inside it. The caller is now free from
checking the errors.
