Added debug output for sed.
Replace /etc/apt/sources.list instead of sed'ing.
Disable sed.
Removed protocol from sources.list configuration.
Added environmental variable for mirror selection.
Merge branch 'fix-debian-mirror'

* fix-debian-mirror:
  Added environmental variable for mirror selection.
  Removed protocol from sources.list configuration.
  Disable sed.
  Replace /etc/apt/sources.list instead of sed'ing.
  Added debug output for sed.