generic driver does not have possibility to disable some of share protocols

[Valeriy Ponomaryov]

Generic driver depends on image.
Image can support limited amount of protocols.
Limited amount of protocols can be used.

But now, Generic driver requires support of NFS and CIFS protocols, but it is not required.
Need to make it possible to define additional configuration option for driver - which protocols are enabled.
In this case driver should not initialize related protocol helper and should not allow to create shares with disabled protocols.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/154106

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/154106
Committed: https://git.openstack.org/cgit/openstack/manila/commit/?id=72bd0df4fe31c57ccd07bef5fa88bf25b14b10a7
Submitter: Jenkins
Branch: master

commit 72bd0df4fe31c57ccd07bef5fa88bf25b14b10a7
Author: Rodrigo Barbieri <email address hidden>
Date: Mon Feb 9 14:10:25 2015 -0200

    Generic Driver image supported protocols

    Currently the generic driver is able to work with any images supplied,
    but it is coded to use always NFS and CIFS helpers in order to interact
    with the image. If a different image is used, for the purpose of other
    share protocols, the above-mentioned helpers may not work. Since
    image selection is up to ADM to set up in manila.conf, the config option
    "share_helpers" should be used to determine which helpers should be
    initialized. Specifying an unsupported combination (helper and image)
    will now print a proper error message during initialization and prevent
    any additional resources from being used.

    Change-Id: If0bebecb5005e4225f9aebc0a8332834d8600a83
    Closes-bug: #1406759