metal3: Rename DISTRIBUTION -> IMAGE_OS

IMAGE_OS is the variable that is used when running the tests, so to
avoid unnecessary variables we want the same variable name here also.

Change-Id: I9ddb64414a142ebd78550c4546dec671f0f791a7
36 files changed
tree: f6e513b762cd68ec5cad555b1ce77f70585a3fb4
  1. jjb/
  2. .gitignore
  3. .gitreview
  4. .yamllint
  5. tox.ini