This detects the 'Darwin' OS family, and uses homebrew to install the
dependencies if so.

This detects the apt-get command, used for installing Ansible, and if it
is missing, displays a message to install it manually first, before
continuing.

This is needed in the get_ansible_remote_environments function.

This checks if the coreutils provided version of ls (installed via brew
`coreutils` package in `ansible/install-dependencies.yml`) exists (i.e.
are we on a Mac), and uses that if available.