[Core] Added --dry-run flag and Travis CI boot test

This should help testing the boot process right until login

.travis.yml

@@ -6,6 +6,7 @@ install:
 script:
   - python -m compileall ./red.py
   - python -m compileall ./cogs
+  - python ./red.py --no-prompt --no-cogs --dry-run
 cache: pip
 notifications:
   email: false

cogs/utils/settings.py

@@ -72,6 +72,11 @@ class Settings:
                             action="store_true",
                             help="Arguments passed and future edits to the "
                                  "settings will not be saved to disk")
+        parser.add_argument("--dry-run",
+                            action="store_true",
+                            help="Makes Red quit with code 0 just before the "
+                                 "login. This is useful for testing the boot "
+                                 "process.")
         parser.add_argument("--debug",
                             action="store_true",
                             help="Enables debug mode")
@@ -92,6 +97,7 @@ class Settings:
         self._memory_only = args.memory_only
         self._no_cogs = args.no_cogs
         self.debug = args.debug
+        self._dry_run = args.dry_run
 
         self.save_settings()
 

red.py

@@ -528,6 +528,10 @@ def main(bot):
         interactive_setup(bot.settings)
     load_cogs(bot)
 
+    if bot.settings._dry_run:
+        print("Quitting: dry run")
+        exit(0)
+
     print("Logging into Discord...")
     bot.uptime = datetime.datetime.utcnow()