Also:

* add keyring file for the salt repo, due to `apt-key` deprecation
* remove old repository file

Use the following command:

```
$ GREP_SED="^\(\s\+master_type: \)true" \
  && grep -rl "${GREP_SED}" test/integration/ \
  | xargs sed -i -e "/${GREP_SED}/s//\1str/"
```

Avoid this error:

```
      ID: salt-master
Function: pkg.installed
  Result: False
 Comment: Error occurred installing package(s). Additional info follows:

   errors:
       - Running scope as unit run-402.scope.
         Loaded plugins: ovl, ulninfo
         https://repo.saltproject.io/py3/redhat/7Server/x86_64/3002/repodata/repomd.xml:
             [Errno 14] HTTPS Error 404 - Not Found
         Trying other mirror.
         No package salt-master available.
         Error: Nothing to do
```

Use the following command:

```
$ GREP_SED="\(repo\.salt\)stack\.com" \
  && grep -rl --exclude-dir=.git "${GREP_SED}" \
  | grep -v .un~$ \
  | xargs sed -i -e "/${GREP_SED}/s//\1project.io/g"
```