title: `apt-get install librdkafka1` fails on Debian 9.x due to libssl dependency
body: <p>Basic <code>apt-get install librdkafka1</code> works on Debian 8.x but fails on Debian 9.x. This looks like a dependency version issue regarding libssl. Debian 8.x had libssl1.0.0 and Debian 9.x has libssl1.0.2 and libssl1.1, but no libssl1.0.0 and this version bump just causes the librdkafka1 install to break.</p>
  
  <p>This is easily reproducible on the latest official Docker Debian 9 image:</p>
  
  <pre><code>docker pull debian:9
  docker run --rm -it debian:9
  </code></pre>
  
  <p>Then within the VM</p>
  
  <pre><code>cat /etc/debian_version
  # 9.4
  
  apt-get update
  # Get basics to setup Confluent repository
  apt-get install -y wget gnupg2 software-properties-common libssl1.0.2
  
  wget -qO - http://packages.confluent.io/deb/4.1/archive.key | apt-key add -
  add-apt-repository "deb [arch=amd64] http://packages.confluent.io/deb/4.1 stable main"
  apt-get update
  </code></pre>
  
  <p><code>apt-cache policy libssl1.0.2</code> results in:</p>
  
  <pre><code>libssl1.0.2:
    Installed: 1.0.2l-2+deb9u3
    Candidate: 1.0.2l-2+deb9u3
    Version table:
   *** 1.0.2l-2+deb9u3 500
          500 http://security.debian.org/debian-security stretch/updates/main amd64 Packages
          100 /var/lib/dpkg/status
       1.0.2l-2+deb9u2 500
          500 http://deb.debian.org/debian stretch/main amd64 Packages
  </code></pre>
  
  <p><code>apt-cache policy librdkafka1</code> results in:</p>
  
  <pre><code>librdkafka1:
    Installed: (none)
    Candidate: 0.11.4~1confluent4.1.0-1
    Version table:
       0.11.4~1confluent4.1.0-1 500
          500 http://packages.confluent.io/deb/4.1 stable/main amd64 Packages
       0.9.3-1 500
          500 http://deb.debian.org/debian stretch/main amd64 Packages
  </code></pre>
  
  <p>And <code>apt-get install librdkafka1</code> results in:</p>
  
  <pre><code>Reading package lists... Done
  Building dependency tree       
  Reading state information... Done
  Some packages could not be installed. This may mean that you have
  requested an impossible situation or if you are using the unstable
  distribution that some required packages have not yet been created
  or been moved out of Incoming.
  The following information may help to resolve the situation:
  
  The following packages have unmet dependencies:
   librdkafka1 : Depends: libssl1.0.0 (&gt;= 1.0.0) but it is not installable
  E: Unable to correct problems, you have held broken packages.
  </code></pre>
  
  <p><code>apt-cache search libssl</code> produces the following. Note that there is a <code>libssl1.0.2</code> and <code>libssl1.1</code> but no <code>libssl1.0.0</code></p>
  
  <pre><code>libssl-ocaml - OCaml bindings for OpenSSL (runtime)
  libssl-ocaml-dev - OCaml bindings for OpenSSL
  libssl-dev - Secure Sockets Layer toolkit - development files
  libssl-doc - Secure Sockets Layer toolkit - development documentation
  libssl1.1 - Secure Sockets Layer toolkit - shared libraries
  libssl1.0-dev - Secure Sockets Layer toolkit - development files
  libssl1.0.2 - Secure Sockets Layer toolkit - shared libraries
  </code></pre>
  
  <p><strong>UPDATE</strong>: This issue is still present with Confluent 4.1, librdkafka 0.11.4 and Debian 9.4.</p>