Making KvsInheritanceTests use backend KVS

The KvsInheritanceTests does not use backend
KVS as identity driver. This patch fix this
by setting it in the config_overrides method.

Change-Id: I45e80e18d7dbcd027493755a8bd30c3fc7e09638
Closes-Bug: 1364618
Merge "Making KvsInheritanceTests use backend KVS"