Output image ID at end of build/push

[bfirsh]

Also -- keep a handle on a unique image name during the build process to
avoid race conditions.

Closes #802

[bfirsh]

@zeke you might want test build and push still work as expected... I haven't fully tested this...

Also not sure if this is the only thing output on stdout. In theory should be, but we might need to clean up some other stuff. There is a test for cog predict that ensures that only output is output on stdout, which is kinda neat.

[zeke]

Works for me! Here's how I tested it:

~/git/replicate/cog output-image-id-at-end-of-build
$ make install
...

~/git/zeke/cog-haiku main
$ cog --version
cog version v0.4.4+dev (built 2022-11-15T15:11:30-0800)

~/git/zeke/cog-haiku main
$ cog push
Building Docker image from environment in cog.yaml as r8.im/zeke/haiku-standard...
...
4ed121b04368: Layer already exists 
d9d07d703dd5: Layer already exists 
latest: digest: sha256:8ab3c4ed267b3badd9ff4b638693a000a19800987a7d863007d5b44df89444c4 size: 3269
Image 'r8.im/zeke/haiku-standard' pushed

Run your model on Replicate:
    https://replicate.com/zeke/haiku-standard
sha256:795173aa5b619f9cdb69d32cd344986327cda5da2d295597ef33b16419128bdc

$ STDOUT=$(cog push)
...

$ echo $STDOUT | tail -n1 |  sed -e 's/sha256://'
91467606ad24771b3a9555f8a30028a6986334b09e0bc2134d70909e6e4550bf

[zeke]

Tested. Works! Seem like we might want some docs for this?

If not, we can document it down the line with CLI docs. #433

[bfirsh]

This is not the only thing output on stdout -- we should fix that. We might also want to remove sha256: prefix.

[bfirsh]

I don't think this does work -- wrong IDs.

[nickstenning]

I guess we're abandoning this for now?