autotest.shared: create a new top level module and namespace

That is intended to be used as a portable (as in easy to sync)
collection of definitions that are needed by separate Autotest
components, such as the RPC server and client.

Signed-off-by: Cleber Rosa <crosa@redhat.com>
Merge pull request #772 from clebergnu/shared_frontend_rpc_v1

autotest.shared: create a new top level module and namespace