! Fix the prometheus_conf_writing_conf macro

[JPLachance]

Greetings!

prometheus-conf started to appear in Falco events as "Write below etc" after an upgrade:

{
    "container.id": "2d3204ad6f6a",
    "evt.time": 1552573221328947059,
    "fd.name": "/etc/prometheus/config_out/rules.tmp/rules-0/system.rules",
    "k8s.ns.name": "monitoring",
    "k8s.pod.name": "prometheus-prometheus-1",
    "proc.aname[2]": "docker-containe",
    "proc.aname[3]": "dockerd",
    "proc.aname[4]": "systemd",
    "proc.cmdline": "prometheus-conf --reload-url=http://localhost:9090/-/reload --config-file=/etc/prometheus/config/prometheus.yaml --rule-list-file=/etc/prometheus/config/configmaps.json --config-envsubst-file=/etc/prometheus/config_out/prometheus.env.yaml --rule-dir=/etc/prometheus/config_out/rules",
    "proc.name": "prometheus-conf",
    "proc.pcmdline": "docker-containe 2d3204ad6f6a8b49d2194c2a8def43034e30f208a2f3525539fd382ce2a0360f /var/run/docker/libcontainerd/2d3204ad6f6a8b49d2194c2a8def43034e30f208a2f3525539fd382ce2a0360f docker-runc",
    "proc.pname": "docker-containe",
    "user.name": "root"
}

This PR updates the existing prometheus_conf_writing_conf macro and fixes the problem.

Enjoy!

[mstemm]

Thanks so much for the changes? Just one thing about parentheses.