<issue_start><issue_comment>Title: Can't upgrade using custom state parition settings
username_0: Running with `rancher.state.dev=LABEL=CUSTOM rancher.state.directory=ros` the upgrade does not find the right device to mount.  Also if it mounts the correct device it probably won't know to touch the files in `/ros/boot` and not `/boot`.
<issue_comment>username_1: I've added some logic for upgrade to try `rancher.state.dev` - but we need to write some code and tests for install to do `rancher.state.directory` and then some tests showing it upgrades.

turns out we also need to add support for gpt booting for this use case.

(probably defering to 0.9.1)
<issue_comment>username_1: this has become less of a priority, as we've solved the problem differently.