tw_cli: tweak VERIFYING state

These commits permit the `tw_cli` plugin to better handle units in the `VERIFYING` state, which should return `OK` by default (following the default value for `--check=`). This pull request also tweaks the output order when multiple controllers or units are present to make the order consistent, and tweaks the `REBUILDING` state to return the `resync` state (although disks will be listed as `DEGRADED` during a rebuild anyway, so the end result is not changed).

Tests have been added/updated and all tests pass following application of all the commits.