The zaqar::server_instance resource type allows setting up multiple
instances of zaqar-server by creating /etc/zaqar/{name}.conf .
Currently there is no validation about the name and if it can be set to
'zaqar' which results in conflicting management of zaqar.conf .
This change introduces a simple validation logic to make sure that
the resource type uses a config file different from the base
zaqar.conf .
Change-Id: Idb0eaff24e84121e0c78daf659d5b9f861491faa
0e7c4f0efe