python-software-properties not found on bionic

It seems python-software-properties was removed from bionic somewhere in the last week or so.

I was bootstrapping fine on Bionic last week, but today while trying to test juju-2.3.6 (proposed) I hit:
2018-04-16 06:01:05 ERROR juju.utils.packaging.manager utils.go:102 packaging command failed: exit status 100; cmd: "apt-get --option=Dpkg::Options::=--force-confold --option=Dpkg::options::=--force-unsafe-io --assume-yes --quiet install python-software-properties"; output: Reading package lists...
Building dependency tree...
Reading state information...
Package python-software-properties 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
However the following packages replace it:
  software-properties-common

E: Package 'python-software-properties' has no installation candidate

I don't know what to make of this:
https://answers.launchpad.net/ubuntu/bionic/+package/python-software-properties

AFAICT, we install it when we are going to use a ppa or some other custom archive source. I don't know what that would be for targeting bionic:
 if len(cfg.PackageSources()) > 0 {
  // Ensure add-apt-repository is available.
  cmds = append(cmds, LogProgressCmd("Installing add-apt-repository"))
  cmds = append(cmds, cfg.paccmder.InstallCmd("python-software-properties"))
 }
 for _, src := range cfg.PackageSources() {
  // PPA keys are obtained by add-apt-repository, from launchpad.
  if !strings.HasPrefix(src.URL, "ppa:") {
   if src.Key != "" {
    key := utils.ShQuote(src.Key)
    cmd := fmt.Sprintf("printf '%%s\\n' %s | apt-key add -", key)
    cmds = append(cmds, cmd)
   }
  }
  cmds = append(cmds, LogProgressCmd("Adding apt repository: %s", src.URL))
  cmds = append(cmds, cfg.paccmder.AddRepositoryCmd(src.URL))
 }

It at least thinks it is necessary to get "add-apt-repository".

I can see that on Bionic we have "add-apt-repository" and it is provided by "software-properties-common":
root@bio:~# dpkg -S /usr/bin/add-apt-repository
software-properties-common: /usr/bin/add-apt-repository

I'm guessing they dropped an old package in Bionic and that broke us.