[cherry-pick] Use numeric uid in Dockerfile (#696) (#699)

/cherry-pick

Signed-off-by: Tamal Saha <tamal@appscode.com>
Co-authored-by: Tamal Saha <tamal@appscode.com>

Author: 1gtm

Dockerfile.in

@@ -46,6 +46,6 @@ RUN set -x \
 COPY --from=0 /restic /bin/restic
 COPY bin/{ARG_OS}_{ARG_ARCH}/{ARG_BIN} /{ARG_BIN}
 
-USER nobody
+USER 65534
 
 ENTRYPOINT ["/{ARG_BIN}"]