[SMAGENT-981] calculate HASH of fedora atomic kernel config

[h-w-chen]

feature

added HASH calculation for fedora atomic linux

how to verify

in AWS start an atomic instance, and start sysdig/agent container in interactive bash session, run /opt/draios/bin/sysdigcloud-probe-loader (or sysdigcloud-probe-loader which contains the added code piece), verified the hash was calculated by having similar output:

* Trying to download precompiled module from https://s3.amazonaws.com/download.draios.com/stable/sysdig-probe-binaries/sysdigcloud-probe--x86_64-4.17.2-200.fc28.x86_64-991367a4c601fb9c7cc8e75487e2b5e6.ko

[bertocci]

In order for this to work in a container, we should need another elif that checks for "${SYSDIG_HOST_ROOT}/usr/lib/modules/${KERNEL_RELEASE}/config" like we do for /boot/config and /usr/lib/ostree-boot/config. How is this working without that?

[h-w-chen]

inside the container, /lib/modules is symlink of $SYSDIG_HOST_ROOT/lib/modules. w/ such symlink in place, the code applies to both native host and container.
see sysdig/docker/local/Dockerfile line 46
RUN ln -s $SYSDIG_HOST_ROOT/lib/modules /lib/modules

this was run inside the container as confirmation of such symlink:
root@ip-172-31-9-169:/# ls -l /lib/modules
lrwxrwxrwx. 1 root root 17 Jun 26 23:50 /lib/modules -> /host/lib/modules

[bertocci]

From slack, we found that this works because /lib is symlinked to /usr/lib in that base image and we set up symlinks in /lib/modules to /$SYSDIG_HOST_ROOT/lib/modules in the docker entrypoint.

To make this robust, let's check /lib/modules/${KERNEL_RELEASE}/config and the same path prefixed with /$SYSDIG_HOST_ROOT. That will still work for the atomic container and will be more flexible in other cases.