Add CRUD methods for tags to the EC2 API.

This is an incomplete implementation of the EC2 tags API.  In EC2, most
resources are able to be tagged.  See
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/Using_Tags.html

In openstack, the only currently 'taggable' resource is an instance, as
it has an instance_metadata table associated.  So far, only instance
tagging has been implemented, but it is relatively simple to extend this
to other resource types by creating the associated model and api calls.

Additionally, in EC2 searches, shell-style globs are allowed, eg:
fo* will match fo, foo, foobar
fo? will match foo

This has been left to do at a later date.

DocImpact: Adds new API calls: CreateTags, DeleteTags, DescribeTags
See:
http://docs.aws.amazon.com/AWSEC2/latest/APIReference/ApiReference-query-CreateTags.html
http://docs.aws.amazon.com/AWSEC2/latest/APIReference/ApiReference-query-DeleteTags.html
http://docs.aws.amazon.com/AWSEC2/latest/APIReference/ApiReference-query-DescribeTags.html

Fixes: bug #1096821
Implements: blueprint ec2-tags-api

Change-Id: Idf1108f6a3476cabdbdb32ff41c00aa4bc2d9ffe
Signed-off-by: Stephen Gran <stephen.gran@guardian.co.uk>
Merge "Add CRUD methods for tags to the EC2 API."