Hart

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Fixed
- Remove an annoying warning for `psutil_compat` from salt.

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Changed
- Swapped to the new Broadcom apt repos for installing salt. Since this repo
doesn't enable pinning salt version in the url, `--salt-branch` was replaced
with `--salt-version` which will be used to set an apt pin for the given
version. This can be either a major version like `3006.*`, or a specific minor
version like `3007.1`.

Added
- Attempt to detect init script failures on GCE (like we do for other providers).

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Added
- Default to adding a `hart-role` label on GCE when creating minion from role.
- `--local-ssds` to automatically attach Local SSD for the GCE provider.
- `-S` or `--script` can now also be passed to create-minion if there's some
setup to be done that is easier to do in a script than through salt.

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Fixed
- Improved resiliency of the default minion config for a saltmaster failover.

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Fixed
- GCP images failing to boot due to picking the wrong architecture for the boot image.

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Changed
- Removed support for classic packages of salt, now only supporting the new onedir
packages. This effectively also limits salt branches to 3005 and 3006, and Debian
versions to buster and newer.