Add user_creds_id to _create_stack RPC interface

Adds the ability to pass the parent user_creds_id into nested stacks
when creating them via RPC, so we can maintain the current behavior
in StackResource, where the parent user_creds record is used by all
nested stacks.

Change-Id: Ifed93860db68a7d23b0c05bd9ec83619e109e386
blueprint: decouple-nested
Implement handle_check for Cinder and EC2 Volumes

This allows OS::Cinder::Volume and AWS::EC2::Volume to perform a sanity
check when performing a stack.check()

Change-Id: I5bb5a25b05391076c998a91f877ccd3986da81ef
Implements: blueprint stack-check
Add requirement to SecurityGroup "remote_group_id"

"remote_group_id" propertie needs to be set only if "remote_mode" is
set to "remote_group_id". If "remote_mode" is in its default value,
remote_group_id is ignored, there is no error message.

There is no clue to understand that remote_mode should be set to
another value, except reading all SecurityGroup properties.
Also, remote_mode does not appear in "neutron security-group-show"
output.

Change-Id: Icdf698a6d7b5539bbc7c4426aa88250229f795f0
Merge "Add requirement to SecurityGroup "remote_group_id""
Merge "Add user_creds_id to _create_stack RPC interface"
Merge "Implement handle_check for Cinder and EC2 Volumes"