"git ubuntu build" uses really long and obscure container name

Working with --keep-build-env is really painful due to the container name. I appreciate that for automation we don't want collisions. But for --keep-build-env, perhaps we could have some option for something smaller (eg. by specifying explicitly in an option), or even default to petname or something?

Use case: the build fails for some reason, and I need to mess inside the build environment to find a fix. Now that I've found a fix, I need to copy my modifications back to the host to test.