pytest: Start nodes with --rescan=1

This shaves off about 15% of our integration testing suite on my machine. It
assumes we never reorg below the first block the node starts with, which is true
for all tests, so it's safe.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

tests/utils.py

@@ -23,6 +23,7 @@ LIGHTNINGD_CONFIG = {
     "cltv-delta": 6,
     "cltv-final": 5,
     "locktime-blocks": 5,
+    "rescan": 1,
 }
 
 DEVELOPER = os.getenv("DEVELOPER", "0") == "1"