Change exec URL-generation to use Ember get (#7963)
Change exec URL-generation to use Ember get (#7963)

This fixes a bug in #7815 where you can’t open an exec window from
the allocation overview because accessing `allocation.job.plainId`
fails across the proxied relationship.
hashicorp/nomad,hashicorp/nomad,burdandrei/nomad,dvusboy/nomad,burdandrei/nomad,dvusboy/nomad,burdandrei/nomad,dvusboy/nomad,dvusboy/nomad,dvusboy/nomad,hashicorp/nomad,hashicorp/nomad,burdandrei/nomad,hashicorp/nomad,burdandrei/nomad,burdandrei/nomad,dvusboy/nomad,dvusboy/nomad,burdandrei/nomad,hashicorp/nomad