Report ping header (destination, packet sizes) as metadata

Signed-off-by: Olivier Mehani <olivier.mehani@nicta.com.au>
Global variables in Ruby are prefixed with $, not @

Signed-off-by: Olivier Mehani <olivier.mehani@nicta.com.au>
Merge branch 'master' of github.com:mytestbed/oml4r
Merge branch 'master' of github.com:mytestbed/oml4r