[20180524143822] Shared Environment and Local Rack Fixes

[ddollar]

You can now specify a global environment: section which will apply to all services:

environment:
  - REQUIRED
  - DEFAULT=value
services:
  web:
    environment:
      - REQUIRED=override
      - DEFAULT=override

• #2688 pass through proper host header [@ddollar]
• #2689 fix linux install paths [@ddollar]
• #2690 use router dns in local rack containers [@ddollar]
• #2691 add shared environment section to manifest [@ddollar]
• #2693 better handling of the case of no local racks installed [@ddollar]