firewall policy update for a rule is not working

If user specifies one rule to update it is not taking but more than one rule
it is accepting as a list and updating the policy. Modified policy-update to
behave same as policy-create command for "--firewall-rules" option

Change-Id: Ia6a1c726be310d60b3b56ce677f843e818079fbe
Closes-bug: 1318617
Merge "firewall policy update for a rule is not working"