In a local development environment, Python tools are loaded from your plugins/tool directory, which you have correctly done. Such local plugins aren't however automatically included in created packages because there is no reliable way to find out what is actually needed by the Python code.
To create a package that contains a Python tool you need to copy the *toolplugin.py file to the analysisapp/ directory of your project. See here for an example. The example contains .tool files, but toolplugin.py files work as well.
One more thing: it is a good idea to register your Python tools with the name of your component as the namespace. That is, if you use "com.acme.python/0" as the namespace, that should also be the full component ID of your component. Importing stuff from other components won't work properly otherwise.
