Add HA enhancement with new "placement_properties" of DEA

Cloud Controller currently does not consider high availability when deploying and scaling applications, which may lead to availability issues even the user has multiple  instances of the application. For example, when all of the application instances are located in one server rack, and this server rack crashed, the whole application system will be unavailable.<br>
This commit adds additional DEA properties named "placement_properties" to identify the location information, for example, which "availability zone" the DEA is located at. Cloud Controller can use this information to distribute the application instances in different "availability zones" to achieve high availability.