THREESCALE-7942 fix apicast bootstrap

[eguzki]

what

removes the warning message at the start of APIcast POD
like this one:

env: '/tmp/FXal6CekIq': Permission denied

verification steps

• start development mode

make development
make dependencies

• Run APIcast

$ cat <<EOF >config.json
{
   "services": [
      {
         "proxy": {
             "hosts": ["one"],
             "proxy_rules": [],
             "api_backend": "https://echo-api.3scale.net",
             "policy_chain": []
         }
      }
   ]
}
EOF

APICAST_LOG_LEVEL=warn APICAST_WORKERS=1 THREESCALE_CONFIG_FILE=config.json BACKEND_ENDPOINT_OVERRIDE=http://localhost:8081 ./bin/apicast

• Check the error env: '/tmp/FXal6CekIq': Permission denied does not exist

[ernaniaz]

Tested here without any problem.