Add proxy support of apt_key module.


Example passing env variables and used by apt_key:
<pre>
vars:
    env:
       http_proxy: "http://http-proxy.local:3128"
       https_proxy: "http://http-proxy.local:3128"
tasks: 
    - name:  install ceph apt-key 
      apt_key: url=https://ceph.com/git/?p=ceph.git;a=blob_plain;f=keys/release.asc state=present 
      environment: $env
</pre>