Prevent loading config twice in K8S

[jvassev]

When config dir is mounted from configmap, filepath.Walk() find the same
.conf file twice as 20-acme.conf is a link to
..data/20-acme.conf for example.

This patch skips all folder names starting with '..' which is pretty
uncommon and mainly used by Kubernetes mounts.

Required for all PRs:

• Signed CLA.
• Associated README.md updated.
• Has appropriate unit tests.

[danielnelson]

Can you give me a brief explanation of why you would have a file layout like this in k8s?

[jvassev]

@danielnelson
When a confimap is mounted, K8S puts the contents in a ..data directory and creates links to the configmap entries. This is how a Prometheus configmap looks like when mounted from the point of view of the container:

ls -la /etc/config/
total 12
drwxrwxrwx    3 root     root          4096 Apr 11 10:57 .
drwxr-xr-x    1 root     root          4096 Mar 28 09:41 ..
drwxr-xr-x    2 root     root          4096 Apr 11 10:57 ..4984_11_04_10_57_03.191612861
lrwxrwxrwx    1 root     root            31 Apr 11 10:57 ..data -> ..4984_11_04_10_57_03.191612861
lrwxrwxrwx    1 root     root            18 Mar 28 09:41 alerts.yaml -> ..data/alerts.yaml
lrwxrwxrwx    1 root     root            21 Mar 28 09:41 prometheus.yml -> ..data/prometheus.yml
lrwxrwxrwx    1 root     root            17 Mar 28 09:41 rules.yaml -> ..data/rules.yaml

If you do a find for rules.yaml, you'll get two matches - something similar happens when telegraf scans the config folder:

find -name rules.yaml
./rules.yaml
./..4984_11_04_10_57_03.191612861/rules.yaml