test images: Adds --force-yes when installing jessie-dnsutils packages

Currently, the jessie-dnsutils image fails to build for arm64 arch with the following
error:

GPG error: http://archive.debian.org jessie Release: The following signatures were invalid: KEYEXPIRED 1587841717

We can bypass this issue by adding a --force-yes flag when installing the needed dnsutils.

Author: claudiubelu

test/images/jessie-dnsutils/Dockerfile

@@ -25,7 +25,7 @@ COPY fixup-apt-list.sh /
 RUN ["/fixup-apt-list.sh"]
 
 RUN apt-get -q update && \
-    apt-get install -y dnsutils && \
+    apt-get install -y --force-yes dnsutils && \
     apt-get clean
 
 ADD https://github.com/coredns/coredns/releases/download/v1.5.0/coredns_1.5.0_linux_BASEARCH.tgz /coredns.tgz