Add shebangs for shellcheck (#4493)

* Add shebangs for shellcheck

See #AR-1406

* Add shebangs for shellcheck

Also for `extensions` scripts

lib/functions/rootfs/apt-install.sh

@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 install_deb_chroot() {
 
 	local package=$1

lib/functions/rootfs/apt-sources.sh

@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 install_ppa_prerequisites() {
 
 	# Myy : So... The whole idea is that, a good bunch of external sources

lib/functions/rootfs/boot_logo.sh

@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 #--------------------------------------------------------------------------------------------------------------------------------
 # Create kernel boot logo from packages/blobs/splash/logo.png and packages/blobs/splash/spinner.gif (animated)
 # and place to the file /lib/firmware/bootsplash

lib/functions/rootfs/create-cache.sh

@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 # get_package_list_hash
 #
 # returns md5 hash for current package list and rootfs cache version

lib/functions/rootfs/customize.sh

@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 customize_image() {
 
 	# for users that need to prepare files at host

lib/functions/rootfs/distro-agnostic.sh

@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 install_common() {
 	display_alert "Applying common tweaks" "" "info"
 

lib/functions/rootfs/distro-specific.sh

@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 install_distribution_specific() {
 
 	display_alert "Applying distribution specific tweaks for" "$RELEASE" "info"

lib/functions/rootfs/post-tweaks.sh

@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 post_debootstrap_tweaks() {
 
 	# remove service start blockers and QEMU binary

lib/functions/rootfs/rootfs-desktop.sh

@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 desktop_postinstall() {
 
 	# disable display manager for the first run