Add VZ ctid to instance_system_metadata

Use instance system_metadata table to store the instance's container
id so it can be retrieved by nova api extensions.

Change-Id: I61ee802942df0c9252d7e28c096a7b1ac41b8fba
Container flavor settings and Vswap

* This allows for defining exact vz configs for specific flavor, instead
  of the driver calculating them.  We can define future vz configs
  through nova flavor extra_specs (metadata) instead of adding configs
  in the driver.

* Vswap has been added as the new default way of setting memory settings

* Refactoring has been done to use new Container class.

Change-Id: I125682bbe89cedec08f328394ebb402a5c079b6d