Enhance the PyPI plugin

[t1m0thyj]

The PyPI package was created quickly to support the Zowe Python SDK repo (#122), but the current implementation is very simple and could be enhanced.

• [ ] Support versioning - currently the Python SDK uses custom scripts to bump the version
• [ ] Check if the package version already exists on PyPI before attempting to publish it
• [ ] Add smoke tests to install the package after it publishes
• [ ] Grab package URL to display in PR comment when publish is successful
• [ ] Implement a better dry run mode - currently it tries to publish to TestPyPI, which likely won't work because token is not the same as for PyPI