Adding loopback commands

Common loopback device commands. Useful for dealing with filesystems
in a file.

loopback_device.sh

+# If an available /dev/loop device is
+# known before running the command
+# losetup /dev/loop0 floppy.img
+
+# Use the first available /dev/loopN device
+losetup -f floppy.img
+
+# Create the filesystem
+mkfs.xfs /dev/loop0
+
+# Destroy loopback device
+losetup -d /dev/loop0
+
+# Mount the loopback image
+mount -o loop -t xfs floppy.img /mnt