share network fields can not be unset after set operation

[Valeriy Ponomaryov]

It is impossible to unset some value from share network if it was set.

See related code: https://github.com/openstack/python-manilaclient/blob/1fba1992/manilaclient/v1/share_networks.py#L121

It should be possible to revert back some changes to share networks as well as for shares and snapshots.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/214573

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/214573
Committed: https://git.openstack.org/cgit/openstack/python-manilaclient/commit/?id=d6ad3710b1a1cd53e1e2f1296ca00f2d2aaddecd
Submitter: Jenkins
Branch: master

commit d6ad3710b1a1cd53e1e2f1296ca00f2d2aaddecd
Author: Julia Varlamova <email address hidden>
Date: Wed Aug 19 07:42:33 2015 -0400

    Allow user to unset share network params

    It is impossible to unset some value from share network if it was set.
    Allow user to set share network params (name, description, neutron_net_id,
    neutron_subnet_id) to empty value.

    Closes-bug: #1446695

    Change-Id: I43315d49a3b721db9619812656702c1865155338