Deploy updates not applied to multisites

[danepowell]

As part of #1092, I thought we had deploy:update running on multisite installs on ACE, but this turned out to be something of a red herring. Using the @sites alias was a good start, but because we also specify drush.uri (https://github.com/acquia/blt/blob/8.x/phing/build.yml#L73), updates only applied to the default site. We need to remove the drush.uri property for this to work.

[bobbygryzynger]

@danepowell - just throwing this out there. Would it suffice to override drush.uri during deploy:update?

<property name="drush.uri" value=""/>

[danepowell]

Yeah actually it might be that simple. I'll open a PR. Thanks!

[grasmash]

Fixed in #1146