Ability to disable rsync options

[benmccann]

rsync_project adds options to rsync such as -p with no way to turn them off. I want to omit some of these options. E.g. -p is making my rsync call fail when syncing to a remote directory that has had acls set with setfacl because the user has permission to write to the directory, but not to change permissions on the files in it.

[bitprophet]

See #910 :)