pytest: test loading all plugins at once, including failing ones.

We modify the slow_init() so it doesn't go too slowly for this test.

This demonstrates a crash, where we currently try to fail a command
multiple times.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tests/plugins/slow_init.py

@@ -1,5 +1,6 @@
 #!/usr/bin/env python3
 from pyln.client import Plugin
+import os
 import time
 
 plugin = Plugin()
@@ -8,7 +9,7 @@ plugin = Plugin()
 @plugin.init()
 def init(options, configuration, plugin):
     plugin.log("slow_init.py initializing {}".format(configuration))
-    time.sleep(21)
+    time.sleep(int(os.getenv('SLOWINIT_TIME', "0")))
 
 
 plugin.run()