Split modifications on datastore root
When we are dealing with modifications, we must not assume they are
not spanning shards. Specifically, we need to make sure we split
data when the user is targeting datastore root, as for those cases
we need to split top-level containers to their appropriate shards,
not the default shard.
JIRA: CONTROLLER-1950
Change-Id: Ie8ad233fed993fddd54a1e4865884fd4474fc81f
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>
(cherry picked from commit
f697416012940c229747715d10d632037e718611)