iscsi_transport parameter should be called iscsi_iface

[Anish Bhatt]

The change https://review.openstack.org/#/c/146233/ added a libvirt parameter called iscsi_transport for open-iscsi transport supports.

We actually need transport_iface, not transport as the param (iscsi_tcp & iser are exceptions to this, where transport and
transport_iface are one and the same), and this is misleading. Giving transport name instead of transport_iface name will also cause login to fail currently, would be better to fall back to iscsi_tcp (also called the default param) when the parameter is incorrect (i.e. the corresponding transport_iface file is non-existent)

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/153743
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=3b8a2cf781d43d0b6937ec66aff5f37657f625ed
Submitter: Jenkins
Branch: master

commit 3b8a2cf781d43d0b6937ec66aff5f37657f625ed
Author: Anish Bhatt <email address hidden>
Date: Fri Feb 6 16:40:36 2015 -0800

    libvirt : Fix slightly misleading parameter name, validate param

    We actually need transport_iface, not transport as the param
    (iscsi_tcp & iser are exceptions to this, where transport and
    transport_iface are one and the same), so change it so that user is
    not confused as to what must be provided. Also fixes a typo in
    param help section.

    Also added code to ensure that non-existing transport_iface is not
    provided, in which case we we log a warning and fall back to the
    default instead of failing as would have previously happened.

    There is no change in functionality, this will just ensure that
    documentation is not misleading.

    Originally added in commit 554647a4deee6ece221eb79fc93551de72b17ae3.

    DocImpact - due to the renamed config option
    Closes-Bug: #1420971
    Change-Id: I6c190328803e8efcde34d522e2c1814ef6afc220