(#7656) Add build action to module_tool face

Before this patch, the module_tool face did not have the ability to
build module release archives, and there was no test coverage for the
module_tool build action.

This patch adds support for building module release archives to the
module_tool face.

Example usage:

$ puppet module_tool build /path/to/module

This patch includes unit tests for the module_tool build action.