Added Docker support (#40)

* Added Docker support

- replaced necessity for devicemapper (through kpartx) by using parted and
  losetup with offsets
- added Dockerfile
- added dependency for parted and grep
- added hints to README.md
- common: loop through unmounts, fix shellcheck warnings

* stage2: use debconf instead of console-setup patch. Fixes #41

scripts/common

@@ -1,10 +1,11 @@
 log (){
-	date +"[%T] $@" | tee -a ${LOG_FILE}
+	date +"[%T] $@" | tee -a "${LOG_FILE}"
 }
 export -f log
 
 bootstrap(){
-	local ARCH=$(dpkg --print-architecture)
+	local ARCH
+	ARCH=$(dpkg --print-architecture)
 
 	export http_proxy=${APT_PROXY}
 
@@ -22,12 +23,12 @@ bootstrap(){
 export -f bootstrap
 
 copy_previous(){
-	if [ ! -d ${PREV_ROOTFS_DIR} ]; then
+	if [ ! -d "${PREV_ROOTFS_DIR}" ]; then
 		echo "Previous stage rootfs not found"
 		false
 	fi
-	mkdir -p ${ROOTFS_DIR}
-	rsync -aHAXx ${PREV_ROOTFS_DIR}/ ${ROOTFS_DIR}/
+	mkdir -p "${ROOTFS_DIR}"
+	rsync -aHAXx "${PREV_ROOTFS_DIR}/" "${ROOTFS_DIR}/"
 }
 export -f copy_previous
 
@@ -38,10 +39,11 @@ unmount(){
 		DIR=$1
 	fi
 
-	while mount | grep -q $DIR; do
-		local LOCS=`mount | grep $DIR | cut -f 3 -d ' ' | sort -r`
+	while mount | grep -q "$DIR"; do
+		local LOCS
+		LOCS=$(mount | grep "$DIR" | cut -f 3 -d ' ' | sort -r)
 		for loc in $LOCS; do
-			umount $loc
+			umount "$loc"
 		done
 	done
 }
@@ -50,42 +52,47 @@ export -f unmount
 unmount_image(){
 	sync
 	sleep 1
-	local LOOP_DEV=$(losetup -j ${1} | cut -f1 -d':')
-	if [ -n "${LOOP_DEV}" ]; then
-		local MOUNTED_DIR=$(mount | grep $(basename ${LOOP_DEV}) | head -n 1 | cut -f 3 -d ' ')
-		if [ -n "${MOUNTED_DIR}" ]; then
-			unmount $(dirname ${MOUNTED_DIR})
+	local LOOP_DEVICES
+	LOOP_DEVICES=$(losetup -j "${1}" | cut -f1 -d':')
+	for LOOP_DEV in ${LOOP_DEVICES}; do
+		if [ -n "${LOOP_DEV}" ]; then
+			local MOUNTED_DIR
+			MOUNTED_DIR=$(mount | grep "$(basename "${LOOP_DEV}")" | head -n 1 | cut -f 3 -d ' ')
+			if [ -n "${MOUNTED_DIR}" ] && [ "${MOUNTED_DIR}" != "/" ]; then
+				unmount "$(dirname "${MOUNTED_DIR}")"
+			fi
+			sleep 1
+			losetup -d "${LOOP_DEV}"
 		fi
-		sleep 1
-		kpartx -ds ${LOOP_DEV}
-		losetup -d ${LOOP_DEV}
-	fi
+	done
 }
 export -f unmount_image
 
 on_chroot() {
-	if ! mount | grep -q `realpath ${ROOTFS_DIR}/proc`; then
-		mount -t proc proc ${ROOTFS_DIR}/proc
+	if ! mount | grep -q "$(realpath "${ROOTFS_DIR}"/proc)"; then
+		mount -t proc proc "${ROOTFS_DIR}/proc"
 	fi
 
-	if ! mount | grep -q `realpath ${ROOTFS_DIR}/dev`; then
-		mount --bind /dev ${ROOTFS_DIR}/dev
+	if ! mount | grep -q "$(realpath "${ROOTFS_DIR}"/dev)"; then
+		mount --bind /dev "${ROOTFS_DIR}/dev"
 	fi
 	
-	if ! mount | grep -q `realpath ${ROOTFS_DIR}/dev/pts`; then
-		mount --bind /dev/pts ${ROOTFS_DIR}/dev/pts
+	if ! mount | grep -q "$(realpath "${ROOTFS_DIR}"/dev/pts)"; then
+		mount --bind /dev/pts "${ROOTFS_DIR}/dev/pts"
 	fi
 
-	if ! mount | grep -q `realpath ${ROOTFS_DIR}/sys`; then
-		mount --bind /sys ${ROOTFS_DIR}/sys
+	if ! mount | grep -q "$(realpath "${ROOTFS_DIR}"/sys)"; then
+		mount --bind /sys "${ROOTFS_DIR}/sys"
 	fi
 
-	capsh --drop=cap_setfcap --chroot=${ROOTFS_DIR}/ -- "$@"
+	capsh --drop=cap_setfcap "--chroot=${ROOTFS_DIR}/" -- "$@"
 }
 export -f on_chroot
 
 update_issue() {
-	local GIT_HASH=$(git rev-parse HEAD)
-	echo -e "Raspberry Pi reference ${IMG_DATE}\nGenerated using pi-gen, https://github.com/RPi-Distro/pi-gen, ${GIT_HASH}, ${1}" > ${ROOTFS_DIR}/etc/rpi-issue
+	local GIT_HASH
+	GIT_HASH=$(git rev-parse HEAD)
+	echo -e "Raspberry Pi reference ${IMG_DATE}\nGenerated using pi-gen, https://github.com/RPi-Distro/pi-gen, ${GIT_HASH}, ${1}" > "${ROOTFS_DIR}/etc/rpi-issue"
 }
 export -f update_issue
+