Add support for non-standard port for rsync

[retlehs]

No option to set a non-standard port for rsync. Ideally this would be parsed automatically from the ssh connection specified in wp-cli.yml

I just hardcoded it into line 184 like so:
rsync -az --progress -e 'ssh -p 18765' "$FROMDIR" "$TODIR"
So obviously not a permanent solution.
@formicagreen