ovs-ofctl: Generalize action and instruction test commands.

ovs-ofctl: Generalize action and instruction test commands.

Until now, there were four of these commands: parse-ofp10-actions,
parse-ofp10-instructions, parse-ofp11-actions, parse-ofp11-instructions.
This is painful to add support for new OpenFlow versions and has a ton of
cut-and-paste code.  This commit generalizes the code to improve on both
of those points.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>