Merge "build_image: Increase spare inodes to 12."

  # increase by > 4% as number of files and directories is not whole picture.

  inodes = output.count('\n')

  spare_inodes = inodes * 4 // 100

  min_spare_inodes = 8

  min_spare_inodes = 12

  if spare_inodes < min_spare_inodes:

    spare_inodes = min_spare_inodes

  return inodes + spare_inodes