Initial changes to remove /boot/common

* find_directory() and hard-coded paths use /boot/system instead of
  /boot/common.
* The build system creates the writable directories in /boot/system
  instead of /boot/common.
* The build system no longer installs any packages in /boot/common.

data/bin/install-wifi-firmwares.sh

@@ -286,7 +286,7 @@ function BuildBroadcomFWCutter()
 
 	# Build b43-fwcutter.
 	echo "Compiling b43-fwcutter for installing Broadcom's firmware ..."
-	make PREFIX=/boot/common CFLAGS="-I. -Wall -D_BSD_SOURCE" > /dev/null 2>&1
+	make PREFIX=/boot/system CFLAGS="-I. -Wall -D_BSD_SOURCE" > /dev/null 2>&1
 	result=$?
 	if [ $result -gt 0 ]; then
 		echo "... failed to compile b43-fwcutter."