install_prerequisites.sh fixes: Prevent need of sudo for dry-runs. Prevent check of whether manually selected package manager exists. Fix dry-run argument location for port.
install_prerequisites.sh fixes: Prevent need of sudo for dry-runs. Prevent check of whether manually selected package manager exists. Fix dry-run argument location for port.

stevenlovegrove/Pangolin,stevenlovegrove/Pangolin,stevenlovegrove/Pangolin