Add command to toggle active container configuration

[mojavelinux]

The Forge Arquillian plugin should have a commnd to toggle the active container configuration. This can be handled in one of two ways:

1. Add the default="true" attribute to the selected container element, removing it from any other container element
2. Writing the qualifier to the file src/test/resources/arquillian.launch, effectively managing this file

I'm imagining something like:

$ arquillian activate-container-configuration --qualifier jbossas-managed-7

The command should also support listing the current active container configuration.

$ arquillian show-active-container-configuration

Managing the active container configuration is a real pain and hard to explain in the guides. Forge support for this task will really help improve the usability of Arquillian.