armbian-next: rootfs: adapt to new reality after huge refactor

- make `tmpfs_estimated_size` and `available_physical_memory_mib` readonly and global and only ever set once
- remove subshell from `get_rootfs_cache_list()`, new version `get_rootfs_cache_list_into_array_variable()` for sanity
- warns if `ROOT_FS_CREATE_ONLY=yes` is set during cached build path
- add a `wait_for_disk_sync()` after restoring rootfs cache
- fix logging sections for `build_rootfs_only()` and `prepare_rootfs_build_params_and_trap()` in `build_rootfs_and_image()`
- remove the logging section from `get_or_create_rootfs_cache_chroot_sdcard()` call in `build_rootfs_only()` (which is now itself logged)
- @TODO: `deploy_qemu_binary_to_chroot()` is leaking a qemu bin in rootfs cache!

lib/functions/rootfs/rootfs-create.sh

@@ -83,7 +83,7 @@ function create_new_rootfs_cache_via_debootstrap() {
 
 	local_apt_deb_cache_prepare "after debootstrap" # just for size reference in logs
 
-	deploy_qemu_binary_to_chroot "${SDCARD}" # this is cleaned-up later by post_debootstrap_tweaks()
+	deploy_qemu_binary_to_chroot "${SDCARD}" # this is cleaned-up later by post_debootstrap_tweaks() @TODO: which is too late for a cache
 
 	display_alert "Installing base system" "Stage 2/2" "info"
 	export if_error_detail_message="Debootstrap second stage failed ${RELEASE} ${DESKTOP_APPGROUPS_SELECTED} ${DESKTOP_ENVIRONMENT} ${BUILD_MINIMAL}"