Catch exceptions thrown while running deferred updates.

Catch exceptions thrown while running deferred updates.

Such exceptions should not reported to the user because the main output
is already sent. Otherwise the user will recive a double reponse with
is just horribly looking. Instead just log these exceptions to keep a
trace of them. This also adds an higher isolation level for these
updates and the post-response cleanup.

Change-Id: I60c2c5ba8ab2ec2d835d8d3042584e98a62809be