Use more specific build output directories

[zmrow]

Issue number:
N/A

Description of changes:
Tuftool currently assumes that all files in the supplied directory are targets for the current repo. We're working on tooling that will help automate the release process and we'll need to handle multiple variants and architectures at once. Moving each arch/variant into its own directory will make it easier to find the relevant files.

We also renamed the build/packages directory to build/rpms to distinguish it from the top level packages directory.

Testing done:

• Build Bottlerocket and everything ends up in the right place!

build/
├── images
│   └── x86_64-aws-k8s-1.15
│       ├── bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-dirty-boot.ext4.lz4
│       ├── bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-dirty-data.img.lz4
│       ├── bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-dirty.img.lz4
│       ├── bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-dirty-migrations.tar
│       ├── bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-dirty-root.ext4.lz4
│       ├── bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-dirty-root.verity.lz4
│       └── latest
│           ├── bottlerocket-aws-k8s-1.15-x86_64-boot.ext4.lz4 -> ../bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-dir4
│           ├── bottlerocket-aws-k8s-1.15-x86_64-data.img.lz4 -> ../bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-dirt4
│           ├── bottlerocket-aws-k8s-1.15-x86_64.img.lz4 -> ../bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-dirty.img4
│           ├── bottlerocket-aws-k8s-1.15-x86_64-migrations.tar -> ../bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-dir
│           ├── bottlerocket-aws-k8s-1.15-x86_64-root.ext4.lz4 -> ../bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-dir4
│           └── bottlerocket-aws-k8s-1.15-x86_64-root.verity.lz4 -> ../bottlerocket-aws-k8s-1.15-x86_64-0.3.4-1ad2043-d4
└── rpms
    ├── bottlerocket-x86_64-acpid-2.0.32-1.x86_64.rpm
    ├── bottlerocket-x86_64-acpid-debuginfo-2.0.32-1.x86_64.rpm
    ├── bottlerocket-x86_64-acpid-debugsource-2.0.32-1.x86_64.rpm
...

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[bcressey]

🌲

[webern]

My precious scriptlets!