bootstrap_host.sh: add guard around traffic forwarding
bootstrap_host.sh: add guard around traffic forwarding

Since it's OS X specific stuff, we don't want it to be run on other
platforms

cuckoobox/cuckoo,cuckoobox/cuckoo,rodionovd/cuckoo-osx-analyzer,rodionovd/cuckoo-osx-analyzer,cuckoobox/cuckoo,cuckoobox/cuckoo,cuckoobox/cuckoo,rodionovd/cuckoo-osx-analyzer