Check instance state before attach/detach interface

Currently there isn't any instance's status checking before
attach/detach interface, It will fail when some status didn't
support it. This patch add checking for it.

This patch allow attach/detach interface for ACTIVE, PAUSED
and STOPPED instance.

* ACTIVE: The interface is hotplug to instance.
* PAUSED: The interface can be hotpluged after instance unpaused.
It's fixed by commit: a868fcedf8e46070cae6aa8e59e61934fa23db1c
* STOPPED: In this status, the instance is destroyed. It just update
the instance configuration with new interface. When the start
instance, the instance will be recreated with new configuration.

Change-Id: I3c038056085be1f655758ed8b6a44bcdbf70cdd5
Closes-bug: #1299333
Merge "Check instance state before attach/detach interface"