Fix incorrect use of getAnchors(dataspace, schemasets)

Fix incorrect use of getAnchors(dataspace, schemasets)

There is an issue in a method deleteDataNodes(dataspace, anchors)
where it doesn't send data update events. This is because it fetches
anchors using a method getAnchors(dataspace, schemaSetNames), when it
needs to fetch anchors by name: getAnchors(dataspace, anchorNames)

Changes:
- Rename getAnchors method using schemasets to getAnchorsBySchemaSetNames
- Add a method getAnchors(dataspace, anchorNames)
- Update test of deleteDataNodes method using getAnchors so it checks
  that data update events are sent

Issue-ID: CPS-2254
Signed-off-by: danielhanrahan <daniel.hanrahan@est.tech>
Change-Id: I55fe853f0a9278a66a5724bf4cf2723b0e2fbc8b