[OHAI-196] work around broken select on older linux kernels

linux kernels prior to 2.6.30 block indefinitely when calling IO.select
on sysfs file descriptors. Using read_nonblock works around this bug.

lib/ohai/plugins/linux/block_device.rb

@@ -25,12 +25,12 @@
     block[dir] = Mash.new
     %w{size removable}.each do |check|
       if File.exists?("/sys/block/#{dir}/#{check}")
-        block[dir][check] = File.read("/sys/block/#{dir}/#{check}").chomp
+        File.open("/sys/block/#{dir}/#{check}") { |f| block[dir][check] = f.read_nonblock(1024).strip }
       end
     end
     %w{model rev state timeout vendor}.each do |check|
       if File.exists?("/sys/block/#{dir}/device/#{check}")
-        block[dir][check] = File.read("/sys/block/#{dir}/device/#{check}").chomp
+        File.open("/sys/block/#{dir}/device/#{check}") { |f| block[dir][check] = f.read_nonblock(1024).strip }
       end
     end
   end