[vbox] update the contrib directory and readme files

[Maksim Malchuk]

Recently we added the contrib directory and the first useful script:
https://review.openstack.org/#/c/323171/
Need to add README.md files and any other useful scripts if exists.

[Bug Checker Bot (bug-checker)]

(This check performed automatically)
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[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/329702

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/329702
Committed: https://git.openstack.org/cgit/openstack/fuel-virtualbox/commit/?id=1f356e5b1b70d43b7c886883689a68fe9bc73ad0
Submitter: Jenkins
Branch: master

commit 1f356e5b1b70d43b7c886883689a68fe9bc73ad0
Author: Maksim Malchuk <email address hidden>
Date: Wed Jun 15 01:46:44 2016 +0300

    Add useful scripts and README.md files

    Please read README.md files for more information.

    Change-Id: I4f65d7ea6c9d9bf8f02d97e63ec09a2f1aae0006
    Closes-Bug: #1592592
    Signed-off-by: Maksim Malchuk <email address hidden>

[Maksim Malchuk (mmalchuk)]

We need to backport this because the original scripts were merged in the Mitaka too: https://review.openstack.org/#/c/324563/

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/mitaka
Review: https://review.openstack.org/329910

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/329910
Committed: https://git.openstack.org/cgit/openstack/fuel-virtualbox/commit/?id=caeb93792328b7ba7d6e19ed722916d89f65f75b
Submitter: Jenkins
Branch: stable/mitaka

commit caeb93792328b7ba7d6e19ed722916d89f65f75b
Author: Maksim Malchuk <email address hidden>
Date: Wed Jun 15 01:46:44 2016 +0300

    Add useful scripts and README.md files

    Please read README.md files for more information.

    Change-Id: I4f65d7ea6c9d9bf8f02d97e63ec09a2f1aae0006
    Closes-Bug: #1592592
    Signed-off-by: Maksim Malchuk <email address hidden>
    (cherry picked from commit 1f356e5b1b70d43b7c886883689a68fe9bc73ad0)