Add bullseye variant with cuttlefish-common

This variant has some more tools which make the rootfs more useful for
development. This rootfs can be used to run cuttlefish (say on GCE, or
under QEMU) or nested under cuttlefish itself. The cuttlefish-common
package is preinstalled to support creating cuttlefish instances.

Change-Id: I1602d2a4ef4501c37616e67862a17902b1e40695