Add mode to metadata header

  -- os-apply-config --
  mode: 0644
  -- end --

Mode must be an integer in [0, 0777]. Preferably this will be written as
three octal digits. The default is to use the mode of the target file if
it already exists, otherwise 0644.

Advances blueprint oac-header

Change-Id: I3abfee89d418474b3766a97cfc178c02252e2d02
Merge "Add mode to metadata header"