Modify doc issues about property option of aggregate
Modify doc issues about property option of aggregate

The formal of multi properties in most docs likes this:
[--property <key=value> [...] ]
[--property <key> [...] ]
This patch modify the formal of multi properties in
aggregate.rst.

Change-Id: I557cd51696d2721c8955c4a79f1ab85de3a0b9ce

dtroyer/python-openstackclient,dtroyer/python-openstackclient,openstack/python-openstackclient,openstack/python-openstackclient