Don't deploy with empty SSH_REMOTE_PATH

[smichaelsen]

If SSH_REMOTE_PATH is not configured, deployment is performed to the initial directory of the SSH user, which is almost always not the desired directory and can result in data loss (because of rsync --delete).
Solution: Don't deploy with empty SSH_REMOTE_PATH. If someone relies on deploying to the home directory, they must explicitly set it.

[smichaelsen]

This is considered a bugfix and not a breaking change, because the documentation explicitly states that the SSH_REMOTE_PATH variable is mandatory.