Handle the case when newModification() fails

Handle the case when newModification() fails

When we are chaining DataTreeModification on top of each other, it is
possible that we have an invalid modification, which fails to apply. In
that case there is nothing we can do, as we cannot establish a baseline.

Handle this case by allocating a specialized modification
implementation, which allows close to no interactions.

JIRA: CONTROLLER-2039
Change-Id: I9b55da7ccc89c9aeae641a049397d2120e292a9c
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>