Use sys.exit(...) instead of exit(...): exit(...) should not be used in programs

contrib/seeds/generate-seeds.py

@@ -114,7 +114,7 @@ def process_nodes(g, f, structname, defaultport):
 def main():
     if len(sys.argv)<2:
         print(('Usage: %s <path_to_nodes_txt>' % sys.argv[0]), file=sys.stderr)
-        exit(1)
+        sys.exit(1)
     g = sys.stdout
     indir = sys.argv[1]
     g.write('#ifndef BITCOIN_CHAINPARAMSSEEDS_H\n')