Pass parameter 'filter' back to model layer

This allows the API to pass back additional arguments to filter search
results by.  This will be useful for resource tagging or other filters.

DocImpact: Adds 'Filter' parameter to DescribeInstance (see
http://docs.aws.amazon.com/AWSEC2/latest/APIReference/ApiReference-query-DescribeInstances.html)

Fixes: bug #922835

Change-Id: I58cc12df650829ed7eb685184a22186d8a5406f4
Signed-off-by: Stephen Gran <stephen.gran@guardian.co.uk>
Merge "Pass parameter 'filter' back to model layer"