Simplify container management by making functions only do one thing

[StayPirate]

The management of the container is currently not optimized due the fact that the logic is part of the sub-functions.
For instance start_container() calls create_container() when it should only start the container.

secbox/secbox

Lines 534 to 544 in eeb5124

	start_container() {
	secbox_container_exists || {
	# If the container does not exist, create it
	print_logo
	msg "${orange}[*]${no_format} ${container} container not found"
	create_container || {
	msg "${red}[!]${no_format} Cannot create the ${container} container"
	return 1
	}
	msg "${green}[.] ${no_format}${container} container created\n"
	}

This generates confusion when other functions calls start_container() and then create_container(), like in update_image():

secbox/secbox

Lines 586 to 596 in eeb5124

	update_image() {
	local _upstream=$(upstream_image_version)
	read -ep "[.] An update is available, do you want to update the container now? [Y/n] " -n 1 -r
	msg "Changelog: https://gitlab.suse.de/security/secbox-image/-/tags/v${_upstream}"
	if [[ ! $REPLY =~ ^[Nn]$ ]]; then
	if pull_image; then
	if secbox_container_exists; then
	if secbox_destroy -f -i; then
	if create_container; then
	start_container
	return 0

Functions need to be rewritten following the UNIX philosophy (or a KISS approach).