Referencing nonexistent schemas on branches 4 and 5

When creating references to schemas we create reference to the schema within the json mime type, which correctly references an existing schema. We do the same for xml mime type except we add the "_xml" suffix.

This is problem as we are not creating schema with such name, so we end up with
incorrect references, thus with incorrect request/response body.

This problem with "_xml" schema references is not present on master branch and neither on the branch 6, but affects branches 4 and 5.

Possible solutions are:

• create the extra schemas that are not created, but are being referenced
  • might be as easy as just creating schema with the "_xml" suffix and make it reference the non-suffixed schema
  • this however will increase our already high number of schemas
• apply change from master that removes "_xml" and "_post" suffixed schemas
  • https://git.opendaylight.org/gerrit/c/netconf/+/105042
  • preferred solution to the previous as it simplifies the whole swagger document and reduces the number of schemas

NOTE:

This is different issue than https://jira.opendaylight.org/browse/NETCONF-1133 , which also deals incorrect schema reference, but that deals with the reference in root POST operation, which affects all branches (this issue affects only branches 4 and 5).