Add aggregate commands

* Add aggregate: add host, create, delete, list remove host, set, show

Bug: 1172032
Blueprint: nova-client

Change-Id: Icd408c2b34af07f5102f53d3778d8546952a12c5
Merge branch 'image-v1' into dt-test
Merge branch 'identity-catalog' into dt-test
Merge branch 'limits-show' into dt-test
Merge branch 'aggregate-commands' into dt-test
Merge branch 'volume-keystone' into dt-test