Add tests for stability handling, fix findings.

[jfdenise]

Tests for stability handling.

• 4 subsystems to cover the 4 known stability levels.
• A common project defining Galleon packages, modules and Galleon features at the 4 known stability level.
• 4 projects to build a feature-pack at a given minimum stability level. Each project includes resources from the common project, so filtering is applied when building the feature-pack to exclude content at a lower stability level.
• Testing the feature-pack content: Must not contain any content at a lower stability level.
• Testing provisioning: The provisioned content must be compliant with the provisioning time stability level (if provided, otherwise must be compliant with the feature-pack minimum stability level).