`helios-build onu` could pick a default boot environment names?

[iximeow]

i'm expecting i will be writing ./tools/helios-build/target/release/helios-build onu -t $(cd projects/illumos/; git describe --long --all HEAD | cut -b 7-) often when hacking on illumos. since projects/illumos is a git repo, it seems workable to use that repo's commit as a default build env name?

this is primarily useful if your projects/illumos is always a clean tree, which is how i expect to interact with projects/illumos: if the defaulting i suggested above sounds plausible, it should come with a very strong warning about dirty files in the tree, lest helios-build pick a boot environment name that suggests it does not contain changes that it does.