return error strings for software update failures

suspect.py

#!/usr/bin/python3

import plistlib, sys

plist = "/System/Library/PrivateFrameworks/SoftwareUpdateMacController.framework/Versions/A/Resources/SUMacControllerError.loctable"

with open(plist, 'rb') as f:
    d = plistlib.load(f)['en']

if len(sys.argv) == 1:
    for k, v in sorted(d.items()):
        print("%s: %s" % (k, v))
    exit(0)

for i in sys.argv[1:]:
    try:
        print("%s: %s" % (i, d[i]))
    except KeyError:
        print("Error: Cannot find code: %s" % i)