cros_image_to_target: Fix --port option
cros_image_to_target: Fix --port option

Previously this script never honored the user --port option.

BUG=None
TEST=Manual: Run with or without --port option

Change-Id: I971ee69818a37e6706ce70327b1d243fd78d214d
Reviewed-on: https://gerrit.chromium.org/gerrit/16429
Reviewed-by: Ryan Cairns <01b618abe573c4fe9e8bd701c0194deadb0e7835@chromium.org>
Commit-Ready: Paul Stewart <3c7b6905653b79322a22957b2a611e2638095229@chromium.org>
Tested-by: Paul Stewart <3c7b6905653b79322a22957b2a611e2638095229@chromium.org>

endocode/scripts,vmware/coreos-scripts,marineam/coreos-scripts,smilart/scripts,sigma/coreos-scripts,trnubo/scripts,BugRoger/scripts,andrejro/coreos--scripts,vmware/coreos-scripts,glevand/coreos--scripts,smilart/scripts,marineam/coreos-scripts,nicescale/scripts,andrejro/coreos--scripts,vmware/coreos-scripts,crawford/scripts,endocode/scripts,fivethreeo/scripts,nicescale/scripts,bcwaldon/coreos-scripts,crawford/scripts,marineam/coreos-scripts,BugRoger/scripts,mischief/scripts,trnubo/scripts,gtank/scripts,zhang0137/scripts,trnubo/scripts,fivethreeo/scripts,BugRoger/scripts,crawford/scripts,smilart/scripts,coreos/scripts,fivethreeo/scripts,gtank/scripts,mjg59/scripts,glevand/coreos--scripts,mischief/scripts,sigma/coreos-scripts,nicescale/scripts,mischief/scripts,sigma/coreos-scripts,gtank/scripts,zhang0137/scripts,endocode/scripts,zhang0137/scripts,mjg59/scripts,bcwaldon/coreos-scripts,mjg59/scripts,coreos/scripts,bcwaldon/coreos-scripts,andrejro/coreos--scripts