We have a few call sites checking the same thing. Make a strong
connection between CopyableNode and CopyHistory -- centralizing
checks and providing an opportunity for optimization.
CopyHistory.contains() now exists only for testing purposes.
JIRA: YANGTOOLS-1215
Change-Id: Ibc9cebe4bee6c5818570c52415c3d8a5ba1ff19d
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit
62c350eff478deeaa90ab0304cdc9c3623c01c83)