test: configure fleet API in functional tests

Needs a bit more context imo. I've been using this script but forgot to add it to the repo
```
; cat functional/run.sh 
#!/bin/bash
#
# WARNING: this script is highly environment-specific and intended to be indicative only. 
# See README.md for more details.
#
export GOROOT="$(pwd)/go"
export PATH="${GOROOT}/bin:$PATH"
cd fleet
ssh-add functional/fixtures/id_rsa
export GOPATH="$(pwd)/gopath"
export FLEETD_BIN="$(pwd)/bin/fleetd"
export FLEETCTL_BIN="$(pwd)/bin/fleetctl"
sudo -E env PATH=$PATH go test github.com/coreos/fleet/functional -v
```