Synchronize uses ~/.ssh/config like Ansible core does

If the user has an ~/.ssh/config file with parameters for the current host, Ansible uses those to connect. Before this change, the synchronize module would fail as it would just fall back to user running the command, provided hostname, default port and no key. I believe this makes the module on par with what the user expects running the rest of Ansible.

Related issue:
https://github.com/ansible/ansible/issues/1171