This commit breaks the large `testChannelBackupRestore` into smaller
tests to take advantage of our parallel testing framework. A smaller
test also makes the debugging easier, hence better code health.
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.
