Improve error code for invalid secret creation with KMIP
Improve error code for invalid secret creation with KMIP

When using KMIP backend, error handling around invalid key
specificaion is modified to return more specific 400 error.

Change-Id: I080aac88c2a055ecfc59e63f840c0d2d12c38d00
Closes-Bug: 1546366

openstack/barbican,openstack/barbican