Avoid create operation on NP containers

[yuekyang]

In the light of current ConfD behavior, it is better to avoid 'create' operation on non-presence containers. More details can be found in the Tail-F ticket PS-47089.

The ticket mentions that the expected behavior of 'delete' operation on non-presence containers is ambiguous. This update avoids 'delete' operation on non-presence containers, too.

Unit test is added.

(pyats-dev) [yuekyang@yangtest-lnx tests]$ python -m unittest test_ncdiff
/auto/ottawa-xe-mpls/users/yuekyang/pyats-dev/github/genielibs/pkgs/conf-pkg/src/genie/libs/conf/device/__init__.py:46: UnsupportedDeviceOsWarning: Device dummy OS is unknown; Extended Device functionality will not be available: mandatory field 'os' was not given in the yaml file
  warnings.warn(
2025-05-02T11:35:07: %NETCONF-INFO: NETCONF CONNECTED
Error in Netconf reply when getting /netconf-state/schemas from YANG module 'ietf-netconf-monitoring':
<rpc-reply xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <rpc-error>
    <error-type>rpc</error-type>
    <error-tag>missing-attribute</error-tag>
    <error-severity>error</error-severity>
    <error-info>
      <bad-attribute>message-id</bad-attribute>
      <bad-element>rpc</bad-element>
    </error-info>
  </rpc-error>
</rpc-reply>

Error in Netconf reply when getting /modules-state/module from YANG module 'ietf-yang-library':
<rpc-reply xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
  <rpc-error>
    <error-type>rpc</error-type>
    <error-tag>missing-attribute</error-tag>
    <error-severity>error</error-severity>
    <error-info>
      <bad-attribute>message-id</bad-attribute>
      <bad-element>rpc</bad-element>
    </error-info>
  </rpc-error>
</rpc-reply>

.......................................
----------------------------------------------------------------------
Ran 39 tests in 0.412s

OK
(pyats-dev) [yuekyang@yangtest-lnx tests]$