Add support for <copy-config> to mdsal-netconf-connector

Motivation

While <edit-config> is enough to configure any Netconf device,

<copy-config> is more user friendly in scenarios, when entire configuration has to be written in single request.

<edit-config> unlike a <copy-config> operation, replaces only the configuration actually present in the <config> parameter.

So user might be required to explicitly delete some nodes that were present in the datastore while flushing netconf device.

Proposed solution

The purpose of the task is to add <copy-config> support to mdsal-netconf-connector which provides northbound server which is a generic interface to MD-SAL in OpenDaylight.

It does not apply to netconf-connector nor config-netconf-connector, so MD-SAL APIs won't be affected.

In order to be consistent with <edit-config>, add support for <candidate/> only.

Support for <running/> might be added in the future as a part of separate task.

<copy-config> handler has to remove old configuration first.

The rest can be seen as simplified version of <edit-config> with "create" operation:

• no need for operation tracking
• no need for special handling for Augmentation/ListSchemaNodes (-NETCONF-385, --NETCONF-427-).

Reference

https://tools.ietf.org/html/rfc6241#section-7.3