Solve the space in base path problem

If there is a space in the base anywhere, the scripts fails to start. 
This is due to the default separator used in bash (which is a space). 
This default separator can be change by setting the variable $IFS.
In `build.sh`, the old IFS variable is saved and then replaced by 
`\n\b`. At the end of the script, the saved IFS is set back.

In `build-docker.sh`, a simple double quote was enough.

build-docker.sh

@@ -41,7 +41,7 @@ if test -z "${CONFIG_FILE}"; then
 	exit 1
 else
 	# shellcheck disable=SC1090
-	source ${CONFIG_FILE}
+	source "${CONFIG_FILE}"
 fi
 
 CONTAINER_NAME=${CONTAINER_NAME:-pigen_work}

build.sh

@@ -229,7 +229,10 @@ fi
 mkdir -p "${WORK_DIR}"
 log "Begin ${BASE_DIR}"
 
-STAGE_LIST=${STAGE_LIST:-${BASE_DIR}/stage*}
+SAVEIFS=$IFS
+IFS=$(echo -en "\n\b")
+
+STAGE_LIST=${STAGE_LIST:-"${BASE_DIR}"/stage*}
 
 for STAGE_DIR in $STAGE_LIST; do
 	STAGE_DIR=$(realpath "${STAGE_DIR}")
@@ -261,3 +264,5 @@ if [ -x ${BASE_DIR}/postrun.sh ]; then
 fi
 
 log "End ${BASE_DIR}"
+
+IFS=$SAVEIFS