MAAS is unable to deploy Eoan to a server using Btrfs

[Rod Smith]

MAAS is unable to deploy Eoan to a server using Btrfs. The deployment log file includes the following error:

Running command ['unshare', '--fork', '--pid', '--', 'chroot', '/tmp/tmpy0cpkf2a/target', 'eatmydata', 'apt-get', '--quiet', '--assume-yes', '--option=Dpkg::options::=--force-unsafe-io', '--option=Dpkg::Options::=--force-confold', 'install', 'btrfs-tools', 'grub-efi-amd64', 'grub-efi-amd64-signed', 'shim-signed'] with allowed return codes [0] (capture=False)
Reading package lists...
Building dependency tree...
Reading state information...
Package btrfs-tools is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'btrfs-tools' has no installation candidate

This works fine when deploying Bionic.

$ dpkg -l '*maas*'|cat
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-===============================-======================================-============-==================================================
ii maas 2.6.1-7832-g17912cdc9-0ubuntu1~18.04.1 all "Metal as a Service" is a physical cloud and IPAM
ii maas-cert-server 0.4.4-0ppa1~git3ac1382~ubuntu18.04.1 all Ubuntu certification support files for MAAS server
ii maas-cli 2.6.1-7832-g17912cdc9-0ubuntu1~18.04.1 all MAAS client and command-line interface
un maas-cluster-controller <none> <none> (no description available)
ii maas-common 2.6.1-7832-g17912cdc9-0ubuntu1~18.04.1 all MAAS server common files
ii maas-dhcp 2.6.1-7832-g17912cdc9-0ubuntu1~18.04.1 all MAAS DHCP server
un maas-dns <none> <none> (no description available)
ii maas-proxy 2.6.1-7832-g17912cdc9-0ubuntu1~18.04.1 all MAAS Caching Proxy
ii maas-rack-controller 2.6.1-7832-g17912cdc9-0ubuntu1~18.04.1 all Rack Controller for MAAS
ii maas-region-api 2.6.1-7832-g17912cdc9-0ubuntu1~18.04.1 all Region controller API service for MAAS
ii maas-region-controller 2.6.1-7832-g17912cdc9-0ubuntu1~18.04.1 all Region Controller for MAAS
un maas-region-controller-min <none> <none> (no description available)
un python-django-maas <none> <none> (no description available)
un python-maas-client <none> <none> (no description available)
un python-maas-provisioningserver <none> <none> (no description available)
ii python3-django-maas 2.6.1-7832-g17912cdc9-0ubuntu1~18.04.1 all MAAS server Django web framework (Python 3)
ii python3-maas-client 2.6.1-7832-g17912cdc9-0ubuntu1~18.04.1 all MAAS python API client (Python 3)
ii python3-maas-provisioningserver 2.6.1-7832-g17912cdc9-0ubuntu1~18.04.1 all MAAS server provisioning libraries (Python 3)

[Alberto Donato (ack)]

This is due to https://bugs.launchpad.net/curtin/+bug/1772618 in curtin