buildserver: handle loops in bash, not ruby, to save memory

buildserver: handle loops in bash, not ruby, to save memory

Apparently, ruby is quite a memory hog when it forks.  I've been getting
errors like this with ./makebuildserver:

Errno::ENOMEM - script[add_btools_17] (android-sdk::default line 72) had an
  error: Errno::ENOMEM: Cannot allocate memory - fork(2)

So instead of looping in ruby and forking for each loop, handle the looping
in the bash script, so ruby is just calling a single bash script.