Improve invalid platform error message
add the minimun required platform to the error message, going from
ERROR:lb-run:current host does not support platform x86_64-slc6-gcc62-opt (dirac_platform: x86_64-slc6, os_id: slc6)
to
ERROR:lb-run:current host does not support platform x86_64-slc6-gcc62-opt (dirac_platform: x86_64-slc6, required: x86_64-slc6.see4_2, os_id: slc6)