Ensure the /lib/modules symlink to /host/lib/modules is set correctly

If /lib/modules exists in the base image, the symlink will get created at
/lib/modules/modules. This removes any existing empty directory but will
fail if we try to remove a non-empty /lib/modules. (Punting on how to
handle non-empty base image dirs for now)

docker/dev/Dockerfile

@@ -48,7 +48,11 @@ RUN curl -s https://s3.amazonaws.com/download.draios.com/DRAIOS-GPG-KEY.public |
  && apt-get clean \
  && rm -rf /var/lib/apt/lists/*
 
-RUN ln -s $SYSDIG_HOST_ROOT/lib/modules /lib/modules
+# Some base images have an empty /lib/modules by default
+# If it's not empty, docker build will fail instead of
+# silently overwriting the existing directory
+RUN rm -df /lib/modules \
+ && ln -s $SYSDIG_HOST_ROOT/lib/modules /lib/modules
 
 COPY ./docker-entrypoint.sh /
 

docker/local/Dockerfile

@@ -41,7 +41,11 @@ RUN rm -rf /usr/bin/clang \
  && ln -s /usr/bin/clang-7 /usr/bin/clang \
  && ln -s /usr/bin/llc-7 /usr/bin/llc
 
-RUN ln -s $SYSDIG_HOST_ROOT/lib/modules /lib/modules
+# Some base images have an empty /lib/modules by default
+# If it's not empty, docker build will fail instead of
+# silently overwriting the existing directory
+RUN rm -df /lib/modules \
+ && ln -s $SYSDIG_HOST_ROOT/lib/modules /lib/modules
 
 ADD falco-${FALCO_VERSION}-x86_64.deb /
 RUN dpkg -i /falco-${FALCO_VERSION}-x86_64.deb

docker/stable/Dockerfile

@@ -47,7 +47,11 @@ RUN curl -s https://s3.amazonaws.com/download.draios.com/DRAIOS-GPG-KEY.public |
  && apt-get clean \
  && rm -rf /var/lib/apt/lists/*
 
-RUN ln -s $SYSDIG_HOST_ROOT/lib/modules /lib/modules
+# Some base images have an empty /lib/modules by default
+# If it's not empty, docker build will fail instead of
+# silently overwriting the existing directory
+RUN rm -df /lib/modules \
+ && ln -s $SYSDIG_HOST_ROOT/lib/modules /lib/modules
 
 COPY ./docker-entrypoint.sh /