storage: Fix the schema and add tests for cifs pool

storage: Fix the schema and add tests for cifs pool

Commit id '887dd362' added support for a netfs pool format type 'cifs'
and 'gluster' in order to add rng support for Samba and glusterfs netfs
pools. Originally, the CIFS type support was added as part of commit
id '61fb6979'. Eventually commit id 'b325be12' fixed the gluster rng
definition to match expectations.

As it turns out the CIFS rng needed a similar change since the directory
path is not an absDirPath, rather just a dirPath will be required.