* This change is only aesthetic (unlike indentation in Python
  tasks).
* Some recipes were using tabs.
* Some were using 8 spaces.
* Some were using mix or different number of spaces.
* Make them consistently use 4 spaces everywhere.
* Yocto styleguide advises to use tabs (but the only reason to keep
  tabs is the need to update a lot of recipes). Lately this advice
  was also merged into the styleguide on the OE wiki.
* Using 4 spaces in both types of tasks is better because it's less
  error prone when someone is not sure if e.g.
  do_generate_toolchain_file() is Python or shell task and also allows
  to highlight every tab used in .bb, .inc, .bbappend, .bbclass as
  potentially bad (shouldn't be used for indenting of multiline
  variable assignments and cannot be used for Python tasks).
* Don't indent closing quote on multiline variables
  we're quite inconsistent wheater it's first character on line
  under opening quote or under first non-whitespace character in
  previous...