setup-environment: automate adding of available multiconfigs to local.conf

This is a second part of the fix for: https://secogroup.atlassian.net/browse/YT-89 (Initial steps to create a combined WIC with FnG System and Yocto)

First part: seco-ne/yocto/layers/meta-seconorth-distro!748 (merged)

In this MR, adjusted setup-environment to automatically:

• find all available multiconfigs and add them to the local.conf before build;
• add "nogpl" layers to bblayers.conf; if multiconfig configuration has been found.