Add sled-agent and maghemite to ZFS image, autoboot sled agent

[smklein]

WARNING: Depends on...

• [buildomat] Package all global zone tarballs into single tarball omicron#2475 (To package global zone services)
• Add the ability to download and unpack prebuilts #56 (To download and unpack global zone services)
• Expand ensure_dir to allow copying subdirectories illumos/image-builder#4 (For ensure_dir pulling in a whole directory)

[jclulow]

I have made a minor change to illumos/image-builder to allow a template to specify an include file by an absolute path, and to allow that absolute path to be provided via a feature flag.

I also took a swing at a basic mechanism for layering on a pre-organised proto area to helios-build experiment-image. If you provide the -P <dir> argument, we'll layer on anything that is under <dir> by generating a partial template for inclusion and passing it to image-builder, with -E so that it can find the files referenced by extsrc in that generated template. Metadata for the files and directories in the manifest are generated by combining the mode bits from the files in the proto area with some heuristics about what the user/group owner should be in the target file system that make sense for our OS image.

If you can modify the omicron PR that produces the archive of Omicron bits that go into the global zone, as per my comment on the PR, then I suspect you'll be able to at least generate an image via:

$ mkdir /tmp/omicron-proto
$ cd /tmp/omicron-proto
$ tar xvfz /tmp/omicron-gz.tar.gz
oxide.json
root/
root/opt/
root/opt/oxide/
...
root/opt/oxide/sled-agent/sled-agent
...
root/lib/svc/manifest/site/sled-agent.xml
...

$ cd ~/helios
$ ./helios-build experiment-image \
    -p helios-netdev=https://pkg.oxide.computer/helios-netdev \
    -F optever=0.21 \
    -B \
    -P /tmp/omicron-proto/root

(Make sure you pull the latest helios.git and run gmake setup to get -P and the image-builder support on which it depends)

[smklein]

@jclulow : I tested this on #56 , using the new package format.

./helios-build experiment-image -p helios-netdev=https://pkg.oxide.computer/helios-netdev -F optever=0.21 -B -P tmp/omicron/global-zone-packages/root

And it seems to build an image without error! Admittedly, I haven't actually unpacked the contents of that image, but this is a start