Necessary word corrections in multiple files

[venkatamahesh]

ReST ==> REST

https://github.com/openstack/magnum/blob/master/doc/source/index.rst

https://github.com/openstack/magnum/blob/master/specs/containers-service.rst

https://github.com/openstack/magnum/blob/master/README.rst

and in search if there are in any other files.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/217327

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/217327
Committed: https://git.openstack.org/cgit/openstack/magnum/commit/?id=c34b8eb1af0fe0bc44ef7a24605d3441185e2c42
Submitter: Jenkins
Branch: master

commit c34b8eb1af0fe0bc44ef7a24605d3441185e2c42
Author: venkatamahesh <email address hidden>
Date: Wed Aug 26 23:25:52 2015 +0530

    Fix the representation of REST

    According to the wikipedia page, Representational
    state transfer should be written as REST but in some
    files it is written as ReST, so I changed it to
    correct one

    Change-Id: I1909b09fbe3e4ed99d817fdaf0006ef55367e74d
    Closes-Bug: #1488816