envsetup: Add support for ZSH

Squash of the following changes:

  Author: Emilio López <turl@tuxfamily.org>
  Date:   Sun Nov 3 13:05:43 2013 -0300

    envsetup: Mark zsh as compatible

    Basic functionality has been tested on zsh 5.0.2 and has been found to
    work correctly.

    Change-Id: I02e5e3bedf56b43104c280d9737ae7b334357643

  Author: Emilio López <turl@tuxfamily.org>
  Date:   Sun Nov 3 13:02:13 2013 -0300

    envsetup: do not print an error if complete fails

    complete is a bashism; so it will fail on other shells. Avoid printing
    an error if that is the case.

    Change-Id: Id6d6311792f409cc3a697c7a2bb003863f1afe60

  Author: Luca Stefani <luca.stefani.ge1@gmail.com>
  Date:   Sun Jul 1 11:26:07 2018 +0200

    Add support for ZSH arrays

    * ZSH arrays are one-based

    Change-Id: Id14396283b77c15e9f0fc6f94628bf312f696006

Change-Id: I4eeea05294fdfcd12f612540d986deb7916c4dff