QbsProjectManager: Implemented retrieval of the Qbs run environment

Adds the environment as defined by Qbs to QtCreator's base environment
when starting a product. This ensures the setupRunEnvironment scripts
are executed and the environment is in the expected state.

Change-Id: I712115a8cf92539d0ce49d0cd61fbe9c6c6fe6ad
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>