`helios-build onu` could be more helpful if asked to package non-built bits

[iximeow]

i built a debug illumos and tried to install it, which went like this:

root@helios:/rpool/devel/oxide/helios# ./tools/helios-build/target/release/helios-build onu -t $(cd projects/illumos/; git describe --long --all HEAD)   
Aug 20 17:52:26.552 INFO creating temporary repository...
Aug 20 17:52:26.552 INFO repository /rpool/devel/oxide/helios/tmp/onu/repo.redist exists, removing first
Aug 20 17:52:27.551 INFO exec: ["/usr/bin/pkgrepo", "create", "/rpool/devel/oxide/helios/tmp/onu/repo.redist"], pwd: None
Aug 20 17:52:27.860 INFO exec: ["/usr/bin/pkgrepo", "add-publisher", "-s", "/rpool/devel/oxide/helios/tmp/onu/repo.redist", "on-nightly"], pwd: None
Aug 20 17:52:28.167 INFO repository /rpool/devel/oxide/helios/tmp/onu/repo.redist for publisher on-nightly created
Aug 20 17:52:28.167 INFO transforming packages for installation...
Aug 20 17:52:28.167 INFO exec: ["/usr/bin/pkgrecv", "-s", "/rpool/devel/oxide/helios/projects/illumos/packages/i386/nightly-nd/repo.redist", "-d", "/rpool/devel/oxide/helios/tmp/onu/repo.redist", "--mog-file", "/rpool/devel/oxide/helios/packages/os-conflicts.mogrify", "--mog-file", "/rpool/devel/oxide/helios/packages/os-deps.mogrify", "-m", "latest", "*"], pwd: None
Aug 20 17:52:28.406 INFO E| pkgrecv: file protocol error: code: E_HTTP_NOT_FOUND (22) reason: The path '/rpool/devel/oxide/helios/projects/illumos/packages/i386/nightly-nd/repo.redist' does not contain a valid package repository.
Aug 20 17:52:28.406 INFO E| Repository URL: 'file:///rpool/devel/oxide/helios/projects/illumos/packages/i386/nightly-nd/repo.redist'.
Error: exec ["/usr/bin/pkgrecv", "-s", "/rpool/devel/oxide/helios/projects/illumos/packages/i386/nightly-nd/repo.redist", "-d", "/rpool/devel/oxide/helios/tmp/onu/repo.redist", "--mog-file", "/rpool/devel/oxide/helios/packages/os-conflicts.mogrify", "--mog-file", "/rpool/devel/oxide/helios/packages/os-deps.mogrify", "-m", "latest", "*"]: failed ExitStatus(unix_wait_status(256))

indeed, packages/i386/nightly-nd does not exist! i've only built debug. it would be nice if helios-build could take a guess that it was giving pkgrecv a bogus path.