Update parallel_emerge to support --force-remote-binary.
Update parallel_emerge to support --force-remote-binary.

This feature is useful if you want to stick to an old binary package of a package you're not working on.

BUG=chromium-os:8769
TEST=./parallel_emerge --board=x86-mario -uDNvg chromeos --force-remote-binary=chromeos-chrome --force-remote-binary=libcros

Change-Id: I7d3011fa64134158ed848f136bc75e09b0af438e

Review URL: http://codereview.chromium.org/4555002

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