A simple proxy client use for testing closed or restricted network
conditions.

This client-forwardproxy works in tandem with the squid-forwardproxy
charm, or any charm that provides forwardproxy. Any Juju application or
provisioned machine can be set up to use the forward proxy like so:

    juju deploy squid-forwardproxy
    juju deploy xenial/ubuntu x1
    juju deploy client-forwardproxy --to 1
    juju add-relation client-forwardproxy:forwardproxy squid-forwardproxy:forwardproxy

The local host and containers on the lxdbr0 are automatically in the
no_proxy list. You can configure additional sites to not proxy.

   juju config client-forwardproxy extra-no-proxy="ubuntu.com canonical.com"

This charm also adds the Ubuntu proposed archive to install and test
optional packages.

    juju config client-forwardproxy proposed-packages="python-boto s3cmd"
