empty value is "-", does not need to be set

[David Lyle]

The default empty value for table cells is "-". This does not need to be specified. See https://github.com/openstack/horizon/blob/master/horizon/tables/base.py#L136 and
https://github.com/openstack/horizon/blob/master/horizon/tables/base.py#L305

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/138797

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/138797
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=5b8170e5bd3fd23d87419a2522c21361cc5b11b6
Submitter: Jenkins
Branch: master

commit 5b8170e5bd3fd23d87419a2522c21361cc5b11b6
Author: David Lyle <email address hidden>
Date: Wed Dec 3 10:24:38 2014 -0700

    Cell empty value defaults to - removing redundancy

    The default value empty_value for a cell is horizon/tables/base.py
    is "-", it is redundant and unnecessary to specify this column
    definitions.

    Closes-Bug: #1398904
    Change-Id: Ica3e8f1559effe6b11f4e81d303758a869acbe2b