Fixes and Improvements for Init-Scripts (Non-Interactive CI-Mode)

This MR introduces a non-interactive mode for the init-env / meta-update scripts. This is meant to be used in automatic CI builds and can be activated by setting an environment variable INITENV_INTERACTIVE to false.
Currently this mode is used to improve performance with shallow clones of meta layers and to fall back to resetting the local branch to the remotes branch in case of conflicts.

There are also some small fixes included that were created along the way.

FYI: @jbauknecht