I have a very standard three node HCI setup running the latest version of oVirt 4.2.  I've been having some problems updating hosts, the last update that was released a few weeks ago would produce installfailed when updating hosts.  I was able to resolve this by rebooting the host first then performing the update.   I eventually got all three hosts updated.  Fast forward to this week, a new update is available.  I've updated engine successfully but first host, I put in to maintenance then updated and the install is failing.  I've rebooted it twice and attempted update again but no go this time.