allow the API to toggle switch ports

[ulrichSchreiner]

This API enables the user to toggle a port of a switch. The endpoint is /switch/{id}/port and the post body contains

type SwitchPortToggleRequest struct {
	NicName string           `json:"nic" description:"the nic of the switch you want to change"`
	Status  SwitchPortStatus `json:"status" description:"sets the port status" enum:"UP|DOWN"`
}

When this endpoint is invoked, the system stores the status as the new desired state (if it differs from the current state). The switch uses metal-core to regularly fetch the switch state. If it finds a desired state which differs from the current state, it will change the switch configuration to reflect this state and send a notification to /switch/{id}/notify and report the new state. If the new state is equal to the desired state, metal-api will store this new state and remove the desired state from the persistence layer.

Dependencies:

• support for switch port toggle on/off metal-core#119
• Toggle switch port metalctl#241

[majst01]

We should run the small integration test suite with this deployed in test, then merge