[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