Client transport options should be configurable

[agis]

The user should be able to specify for example flags passed to rsync and also the source directories.

[agis]

I think this should be provided for cases where more control over how the transports are used is required. An idea that just popped to mind:

$ mistry build --project foo --transport-command "rsync -avP --delete $source /tmp/foobar"

This way, the user gets full control over the command that's going to be called. The $source part is a variable that we'll parse and substitute with the actual source (eg. mistry.myapp.com:/var/lib/mistry/data/foo/ready/12332).