Don't process ~/.ssh/config

Brad reported that sync-dir wasn't working. Upon investigation, it turned out
that his ~/.ssh/config included configuration options that had a higher
priority than command-line options. To prevent this from being an issue, we
need to instruct ssh to not process configuration directives from
~/.ssh/config.

Change-Id: Id7495d1cfc44cc6dc593f80450c3937d2a395205