Caching for EC2 metadata requests - EUCA-8732

EUCA-8732
Network configuration JSON Cluster property now optional - EUCA-9116

The cluster property for JSON network configuration is now optional. The
behaviour is the same if the property is omitted or the clusters list is
empty.

EUCA-9116
Add HTTP connection close header for metadata responses - EUCA-8448

EUCA-8448
Use the registered host for user facing services in eucarc - EUCA-9117

EUCA-9117
Merge remote-tracking branch 'origin/dev/sjones/EUCA-8732' into testing
Merge remote-tracking branch 'origin/dev/sjones/EUCA-9116' into testing
Merge remote-tracking branch 'origin/dev/sjones/EUCA-9117' into testing