Use GNU tar in the Docker image

The busybox implementation of tar doesn't support the
`--ignore-failed-read`, which is used when the VolumeSnapshotClass has
the `ignoreFailedRead` parameter set to `true`.

This patch uses the GNU implementation of tar, which implement that.

Author: leonardoce

Dockerfile

@@ -18,6 +18,6 @@ LABEL description="HostPath Driver"
 ARG binary=./bin/hostpathplugin
 
 # Add util-linux to get a new version of losetup.
-RUN apk add util-linux coreutils socat && apk update && apk upgrade
+RUN apk add util-linux coreutils socat tar && apk update && apk upgrade
 COPY ${binary} /hostpathplugin
 ENTRYPOINT ["/hostpathplugin"]