Use find to delete files recursively (#4732)

* Use find to delete files recursively

Instead of using rm -rf use find to delete files recursively. This
has the added benefit that we do not need to rely on shell expansion.

In particular, shell expansion caused the --one-file-system flag to
not work as intended: The idea was that the content of a (left-over)
bind mounted directory would not get deleted. However, since shell
expansion passed the directory to rm, rm happily deleted also files in
that bind mounted directory.

* Pass arguments correctly

* Fix argument order and stderr output

* Improve error handling

Log with exception level if there is an OS level error. Decode the
stderr output correctly.

* Remove unnecessary newline

Dockerfile

@@ -15,7 +15,7 @@ WORKDIR /usr/src
 RUN \
     set -x \
     && apk add --no-cache \
-        coreutils \
+        findutils \
         eudev \
         eudev-libs \
         git \