Today UUIDField emits a warning if the provided value is not a valid
UUID. However this warning cannot be escalated to an exception through
the standard warnings module because the validation code also adds a
warning filter to the warning filter list that overrides the existing
filters.
This patch ensures that the 'once' warning filter only added to the
end of the filter list. This way if the client has already specified
another filter for this warning (e.g. and error filter) then that
filter will not be overriden.
Change-Id: I17cb96d16fcd91195478b738fbdda01b47cfd69d
Closes-Bug: #1746966
0e3526710f