When you want to quickly boot from a drive or image in a virtual machine you do not need to setup up a VirtualBox machine. Often QEMU does the job well enough.

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Install it:

sudo apt-get install qemu

To boot an ISO:

qemu-system-x86_64 -cdrom filename.iso

If you prepared a USB pen drive and want to test it, run it like this (/dev/sdx being your device name; you may need to sudo to access it):

qemu-system-x86_64 -hda /dev/sdx

Be aware that not everything runs smoothly in QEMU -- you might need to set up a VirtualBox for complex scenarios.

On older Ubuntus, you could still say qemu where it's now qemu-system-x86_64 or qemu-system-i386.