Fix KeyError while generating a WSGI response

The KeyError exception raised while generating a WSGI response based on
the 413 exception. Because there may be no "Retry-After" attribute in the
exception headers.

Change-Id: I89eb1878acc2195775be17fbcba8088f2e00bac1
Closes-Bug: #1259867
make delete recovery messages debug level

lvm.delete has recovery logic within it to do a second attempt
if it should fail the first time. It is currently however logging
those second attempts at error and warn levels. However, as this
is normal flow these should be debug level instead.

This is currently causing a few resets in the gate because this
is a non whitelisted error.

Change-Id: Ie684331d9d97c089ec23569d06981e90eb7f6a67
Closes-Bug: #1261731
Merge "Fix KeyError while generating a WSGI response"
Merge "make delete recovery messages debug level"