Add support for key_list parm to sprint_varx and sprint_var
Add support for key_list parm to sprint_varx and sprint_var

- key_list is a list of keys from a dictionary which are to be
  printed.  All other keys are skipped.  If key_list is None, then
  all keys are printed.

Change-Id: Ib4fb48114ca3880bfa38d494de3ede4fdeea023a
Signed-off-by: Michael Walsh <10404802c7de463f402c4a18638106ca1b12ef61@us.ibm.com>

openbmc/openbmc-test-automation,openbmc/openbmc-test-automation