Now /graphs/execute/ handler is used to execute graph

[OpenStack Infra]

https://review.openstack.org/360136
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.

commit 3e421cdd3ecf22f07d213fe5b82b4ecf4af6cb9f
Author: Ilya Kutukov <email address hidden>
Date: Wed Jul 27 14:30:27 2016 +0300

    Now /graphs/execute/ handler is used to execute graph

    $ fuel2 graph execute --env 1 [--nodes 1 2 3] [--graph_types gtype1 gtype2] [--task-names task1 task2] [--force] [--dry-run]
    now calling brand new:
    /api/v1/graphs/execute/
    handler that using the Transactions Manager.

    Also now it is possible to call:

    $ fuel2 graph execute --force
    to enforce execution of tasks without skipping.

    $ fuel2 graph execute --task-names task1 task2
    to run only specific tasks ignoring dependancies.

    DocImpact
    Change-Id: Iafc59c60a1ebce4a360ce1faa00a27ab320fa90b
    Implements: blueprint graph-concept-extension
    (cherry picked from commit 98e45a0317a1482e6ac1e3b5950c741f3432775a)