Add additional info to resource provider aggregates update API
Add additional info to resource provider aggregates update API

Mention that if any nonexistent aggregate uuids are provided, those
aggregates will be created automatically first during the update call.
I think this is a good addition since in fact I was much confused how
the aggregates can be created in the first place when playing with
the placement APIs.

Change-Id: I2f86715a21784eb974b73fc3edc74eedd73ad48b

gooddata/openstack-nova,openstack/nova,gooddata/openstack-nova,klmitch/nova,rahulunair/nova,openstack/nova,rahulunair/nova,gooddata/openstack-nova,gooddata/openstack-nova,klmitch/nova,klmitch/nova,rahulunair/nova,mikalstill/nova,mahak/nova,mikalstill/nova,mahak/nova,openstack/nova,klmitch/nova,mikalstill/nova,mahak/nova