Adds more validations in create_snapshot
Adds more validations in create_snapshot

This patch adds more validations in create snapshot, like
host and replication. And removes the check logic
in create_snapshot_in_db method.

Change-Id: I8e5c7664e54116cc9e302e5e7903f4d7b04c836c

mahak/cinder,openstack/cinder,mahak/cinder,openstack/cinder