Unify main:

- same multiprocessing start method for start.sh and setuptools entry point,
 - make it possible to run outside of the main thread.

minode/main.py

@@ -263,9 +263,7 @@ def start_i2p_listener():
 
 
 def main():
-    signal.signal(signal.SIGINT, handler)
+    multiprocessing.set_start_method('spawn')
-    signal.signal(signal.SIGTERM, handler)
-
     parse_arguments()
 
     logging.basicConfig(
@@ -273,6 +271,12 @@ def main():
         format='[%(asctime)s] [%(levelname)s] %(message)s')
     logging.info('Starting MiNode')
 
+    try:
+        signal.signal(signal.SIGINT, handler)
+        signal.signal(signal.SIGTERM, handler)
+    except ValueError:
+        logging.warning('Working outside of the main thread!')
+
     logging.info('Data directory: %s', shared.data_directory)
     if not os.path.exists(shared.data_directory):
         try:
@@ -315,5 +319,4 @@ def main():
 
 
 if __name__ == '__main__':
-    multiprocessing.set_start_method('spawn')
     main()