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