Caveats:
* TLS files must be present on the target server (and readable)
* TLS file paths cannot contain spaces
* TLS file paths must be absolute (i.e. cannot be relative)
* Bash argument parsing is terrible
Due to https://github.com/docker/docker/issues/9098, there is no way to
signal an exec. Instead we'll have to just poll the interface and hope.
Adds `weavewait -s` which is the way to tell weavewait to skip waiting
for a signal, which we use on execs
Paul Bellamy