Make sure checks.d directory is present

[ghost]

What does this PR do?

It makes sure the checks.d directory is present in the container.

Motivation

Otherwise the following copy command will create a file called 'checks.d' for the first check file.

We weren't previously able to mount a checks.d directory as a volume. The mounting-as-a-volume part worked, but the copying-to-the-actual-directory part was broken because the target checks.d directory within the container didn't exist.

[xvello]

Hi @lgierth and thank you for your contribution. Indeed this is a bug in the current entrypoints.

• To be consistent with how we handle /conf.d, I'd go with
  find /checks.d -name '*.py' -exec cp --parents {} /opt/datadog-agent/agent \;
  instead. This makes cp create the parent folder if needed (and it is indeed needed). Would that be OK with you?

• You PR patches two entrypoints, but we have a third one in jmx/entrypoint.sh. Could you please include this one as well?

Regards

[aerostitch]

@xvello I noticed this issue during the refactoring of the entrypoints in #222 and am fixing it there with --parents. (just FYI).

[ghost]

Hey sorry I totally forgot about this -- crazy busy times right now. @aerostitch thanks!