use DEA/Warden snapshotting in drain script

Now sends USR1 once, and backs off until all staging tasks complete.
After that, sends USR2 to Warden, and kill -9's the DEA. No evacuation
is performed. Both jobs will come up and repopulate their state via
their respective snapshot loading mechanisms.

If the job is going to be shut down, execute the existing evacuation
strategy, and wait 2 minutes.
fix dea_next drain.rb template spec
fix dea drain script
Bump src/cloud_controller_ng, src/dea_next

Bump cloudfoundry/cloud_controller_ng:
  Alex Suraci and Maria Shaldibina:
     updating an app's routes sets a new version ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12300190 )
  Cornelia Davis and Jimmy Da:
     Make syslog_drain_url optional ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12295325 )
  Mark Rushakoff and Ruth Byers:
     Clear database before apps api spec ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12292888 )
     Remove stray print from test ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12249113 )
     Admin buildpacks must have a key ( Travis Unknown )
  Ian Lesperance and Jeff Schnitzer:
     Imports tags from v2 service broker catalog. ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12282291 )
     Forward the broker error description, if present ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12281679 )
     Abandon vcap-common ServiceGatewayClient. ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12254960 )
     Verify request headers for all v2 client commands ( Travis Unknown )
  Casey McTaggart:
     Bump loggregator_emitter version ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12277329 )
  Julz Friedman and Tim Labeeuw:
     Don't autogenerate the fields documentation. We prob need a test that ensures all fields are included ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12242873 )
Bump cloudfoundry/dea_ng:
  Alex Suraci and Maria Shaldibina:
     update running version if included in dea.update ( Travis Success: https://travis-ci.org/cloudfoundry/dea_ng/builds/12298722 )
     Stop sending advertisements in response to USR1 ( Travis Unknown )
warden: don't destroy containers on startup

We're using the snapshot feature again, so this is counterproductive.

Old containers should be destroyed via the grace period if no one's
actually talking to them.
rebase on master
runner: allow max_in_flight to be overridden
Bump src/cloud_controller_ng, src/dea_next

Bump cloudfoundry/cloud_controller_ng:
  Alex Suraci and Maria Shaldibina:
     updating an app's routes sets a new version ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12341901 )
     send nil download URI if local blob doesn't exist ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12341889 )
  Tim Labeeuw:
     Change the POST /v2/buildpacks/<guid>/bits to a PUT to match the app bits upload and since semantically we are replacing not adding the buildpack bits. ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12340990 )
  Julz Friedman and Tim Labeeuw:
     The bootstrap CSS should loaded with no scheme so that it works on http and https. ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12334293 )
     Correct the output when downloading a droplet or buildpack cache ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12334030 )
     Futher fixes to the api docs ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/12333764 )
     Exclude the buildpacks which haven't been uploaded yet from the staging message ( Travis Unknown )
     Staging message admin buildpack list is ordered by priority ( Travis Unknown )
     Finish up adding fields to the api docs ( Travis Unknown )
Bump cloudfoundry/dea_ng:
  Alex Suraci and Maria Shaldibina:
     update running version if included in dea.update ( Travis created: https://travis-ci.org/cloudfoundry/dea_ng/builds/12342613 )
     Stop sending advertisements in response to USR1 ( Travis Unknown )
     load from snapshots again, snapshot staging tasks ( Travis Unknown )
     create buildpack cache file only if downloaded ( Travis created: https://travis-ci.org/cloudfoundry/dea_ng/builds/12342599 )
Bump src/dea_next

Bump cloudfoundry/dea_ng:
  Alex Suraci and Maria Shaldibina:
     update running version if included in dea.update ( Travis started: https://travis-ci.org/cloudfoundry/dea_ng/builds/12347091 )
     Stop sending advertisements in response to USR1 ( Travis Unknown )
     load from snapshots again, snapshot staging tasks ( Travis Unknown )
     create app package file only if downloaded ( Travis started: https://travis-ci.org/cloudfoundry/dea_ng/builds/12347084 )
     correct parallel droplet downloading ( Travis Unknown )
  Tim Labeeuw:
     Move around the DEA to be in better folders ( Travis Failed: https://travis-ci.org/cloudfoundry/dea_ng/builds/12346237 )