Add drush local support to the Pantheon Backdrop CMS upstream.

[serundeputy]

This adds:

• drush toBACKDROP_ROOT/drush/drush
• backdrop drush extension in BACKDROP_ROOT/drush/drush/commands/backdrop
• Drush executable is at BACKDROP_ROOT/drush/drush/drush

---

PR from @serundeputy at #7
PR from @jenlampton at #8
PR from @herbdool at #25
PR from @jenlampton at #65

[jenlampton]

After applying the PR as-is and trying a drush cc all on my local I get:

sh: /.../backdrop/drush/drush/drush.launcher: Permission denied

so I tried changing permissions on my local /drush/ to 775, and then got this error with a drush cc all:

Fatal error: Class 'Robo\Robo' not found in /.../backdrop/drush/drush/includes/preflight.inc on line 243

pushing to pantheon and running the same command terminus drush cc all gives an equivalent error:

Fatal error: Uncaught Error: Class 'Robo\Robo' not found in /srv/bindings/67212ef6bf624df8922f0463000bd130/code/drush/drush/includes/preflight.inc:243
Stack trace:
#0 /srv/bindings/67212ef6bf624df8922f0463000bd130/code/drush/drush/includes/preflight.inc(187): drush_init_dependency_injection_container()
#1 /srv/bindings/67212ef6bf624df8922f0463000bd130/code/drush/drush/includes/preflight.inc(35): drush_preflight_prepare()
#2 /srv/bindings/67212ef6bf624df8922f0463000bd130/code/drush/drush/drush.php(12): drush_main()
#3 {main}
  thrown in /srv/bindings/67212ef6bf624df8922f0463000bd130/code/drush/drush/includes/preflight.inc on line 243
Ok

Reverting this commit (but leaving the pantheon.yml file) and running terminus drush cc all behaves as expected, can't find "Drupal":

No Drupal site found, only 'drush' cache was cleared.

and to confirm we have drush 8 I did drush @pantheon.mysite.dev status and got

PHP executable      :  /srv/bindings/67212ef6bf624df8922f0463000bd130/php/php 
 PHP configuration   :  /srv/bindings/67212ef6bf624df8922f0463000bd130/php.ini 
 PHP OS              :  Linux                                                  
 Drush script        :  /opt/pantheon/drush-8/drush.php                        
 Drush version       :  8.0.5                                                  
 Drush temp          :  /tmp                                                   
 directory                                                                     
 Drush               :  /srv/bindings/67212ef6bf624df8922f0463000bd130/.drush/ 
 configuration          drushrc.php /etc/drush/drush8rc.php                    

Also, my Local site is functional again, drush cc all clears caches:

'all' cache was cleared.   

[jenlampton]

Digging deeper, the version of drush that I am running on my local (8.2-dev) doesn't have use Robo\Robo; in its preflight.inc. What I see in that file is use Drush\Log\LogLevel; and nothing after that. I can't get this version of drush to tell me which version it is, but I suspect it might be Drush 9? Here's drush 8 from the source: https://github.com/drush-ops/drush/blob/8.x/includes/preflight.inc

[jenlampton]

I just filed a new PR with the 8.x branch of drush. this one actually clears my caches! :)

[2016-09-23 04:18:36] [info] Running drush cc all on mysite-dev
    cmd: 'cc all'
    site: 'mysite'
    env: 'dev'
'all' cache was cleared.