This means that Jython cannot find the 'django' module. Here, the first thing Jython is going to do is try to find the django module:
from django.core.management import execute_manager
It fails, and throws ImportError: No module named django.
You should find out where your django module is, it should be a directory named 'django' that contains an __init__.py file.
Set your python path for jython to the parent directory. For example, if you find /Users/cassiomelo/code/jython/Lib/site-packages/django/__init__.py, then you should add /Users/cassiomelo/code/jython/Lib/site-packages to the python path. Click the link to see how to set it depending on your Jython version.
The next time Jython will try to import the 'django' module, it will look in the directory of the python path if there is a directory named 'django' with an __init__.py in it and proceed to importing the core submodule, then management, then execute_manager.