* internal/host/plugin: add UpdateSet
This adds the UpdateSet repository function.
UpdateSet runs the OnUpdateSet plugin call within the transaction as per
the changes in #1683.
The plugin call returns the updated set, the hosts in the set, the rows
updated, and any error.
* Ensure that attributes can be cleared by supplying a full null
* move version increment to the end and track perferred endpoint update separately
* move plugin call to end of transaction
* only clone returned set once, and move host fetch call out of transaction
* Request a sync when attributes are updated
* Add test to assert that old preferred endpoints are being removed correctly
Chris Marchesi
c2cd6febca