hs-test: use equal ubuntu versions in test images

Official nginx image is based on Debian with older libc version,
that causes a runtime fail when VPP libraries are compiled in Ubuntu
which has newer libc.
Using equal version of Ubuntu in VPP image and in nginx image
ensures that running nginx won't fail due to different libc versions.

Type: test
Signed-off-by: Maros Ondrejicka <maros.ondrejicka@pantheon.tech>
Change-Id: I48f3b23be30a9d9d9144351437ce163d64a4bb6b
diff --git a/extras/hs-test/Dockerfile.vpp b/extras/hs-test/Dockerfile.vpp
index 45b6287..f95df22 100644
--- a/extras/hs-test/Dockerfile.vpp
+++ b/extras/hs-test/Dockerfile.vpp
@@ -1,4 +1,6 @@
-FROM ubuntu:22.04
+ARG UBUNTU_VERSION
+
+FROM ubuntu:${UBUNTU_VERSION}
 
 RUN apt-get update \
  && apt-get install -y openssl libapr1 libnuma1 libsubunit0 \