report optimal io size for block devices

LVM aligns devices data area to io hints, reported for
block devices. Optimal io size can be big for some devices
(16M, as reported in bug). So nailgun's volume manager
should take it into account while doing partitioning.
So nailgun-agent should send this information to nailgun.

Change-Id: Idd9b778f7f21d4fe9d3fd029038664de41f93447
Partial-Bug: #1546049

agent

@@ -481,7 +481,8 @@ class NodeAgent
               :disk => block[:disk],
               :extra => block[:extra],
               :removable => block[:removable],
-              :paths => nil
+              :paths => nil,
+              :opt_io => get_opt_io.fetch(dname, block_size)
             }
 
           elsif @mpath_devices.has_key?(dname)
@@ -733,6 +734,26 @@ class NodeAgent
     @blocks
   end
 
+  def get_opt_io
+    return @opt_io_res if defined?(@opt_io_res)
+
+    @opt_io_res = {}
+
+    # example output:
+    # sda    4096      0
+    # sdb     512      2048
+    output = `lsblk --nodeps --bytes --noheadings --output NAME,MIN-IO,OPT-IO`
+    output.split("\n").each do |line|
+      name, min_io, opt_io = line.split()
+      @opt_io_res[name] = opt_io.to_i != 0 ? opt_io.to_i : min_io.to_i
+    end
+
+    @opt_io_res
+  rescue => e
+    @logger.error("Error '#{e.message}' in obtaining optimal io size: #{e.backtrace}")
+    @opt_io_res ||= {}
+  end
+
   def _is_virtualbox
     @os[:dmi][:system][:product_name] == "VirtualBox" rescue false
   end