install: Make Debian install fully non-interactive
Although the installation instructions specify `apt-get -y ...`, the
installation blocks when trying to install the Kata pages with a message
like this:
```
...
Restart services during package upgrades without asking?
<Yes>                                          <No>
```
Setting `DEBIAN_FRONTEND=noninteractive` avoids this.
Fixes
2. Install the Kata Containers components with the following commands:
```bash
+ $ export DEBIAN_FRONTEND=noninteractive
$ ARCH=$(arch)
$ source /etc/os-release
$ sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/katacontainers:/releases:/${ARCH}:/master/Debian_${VERSION_ID}/ /' > /etc/apt/sources.list.d/kata-containers.list"
