Add fuel2 commands to operate on extensions

[OpenStack Infra]

https://review.openstack.org/356591
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.

commit ea08c45295b788d9f51fd4d969a4235f221ba3aa
Author: Alexander Gordeev <email address hidden>
Date: Wed Aug 31 20:59:21 2016 +0300

    Add fuel2 commands to operate on extensions

    Releases new fuel2 commands to operate on extensions:
        fuel2 env extension enable
        fuel2 env extension disable
        fuel2 env extension show
        fuel2 extension list

    DocImpact

    Also, this change introduces the option for BaseListCommand for
    specifying the default fields to sort by.

    Change-Id: Idee06633689efece18838766de5c4afcd24190d7
    Implements: blueprint extensions-management
    Partial-Bug: #1614526

[Olena Logvinova (ologvinova)]

Fix proposed to branch: master
Review: https://review.openstack.org/#/c/369298

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/369298
Committed: https://git.openstack.org/cgit/openstack/fuel-docs/commit/?id=87b50fe4062cf6bebf016b58eaa5aa9351890de5
Submitter: Jenkins
Branch: master

commit 87b50fe4062cf6bebf016b58eaa5aa9351890de5
Author: Olena Logvinova <email address hidden>
Date: Tue Sep 13 12:46:45 2016 +0300

    [UG] [CLI] Consolidated Fuel CLIs v1 and v2

    This patch:

    - adds a deprecation note for Fuel CLI v1 to the
      Fuel CLI section of the Fuel User Guide;
    - adds a table with consolidated fuel and fuel2
      commands;
    - fixes noticed typos and formatting discrepancies.

    Change-Id: Ibb005e3ecc4d094229f9b7c951a92fe9e5d6574e
    Closes-Bug: #1608883
    Closes-Bug: #1609815
    Closes-Bug: #1619200
    Closes-Bug: #1618873
    Closes-Bug: #1618456
    Closes-Bug: #1612611
    Closes-Bug: #1612609
    Closes-Bug: #1611835
    Closes-Bug: #1612148
    Closes-Bug: #1612151
    Closes-Bug: #1612218
    Closes-Bug: #1612610
    Closes-Bug: #1612606
    Closes-Bug: #1612607
    Closes-Bug: #1612227
    Closes-Bug: #1621807
    Closes-Bug: #1621838
    Closes-Bug: #1623595
    Closes-Bug: #1612608
    Closes-Bug: #1619290
    Closes-Bug: #1612598
    Closes-Bug: #1624044