hs-test: autodetect ubuntu version during build

Since VPP binaries are being compiled on host system,
it makes sense to autodetect Ubuntu version when building test images
so that containers would be running version equal to host system.

Type: test
Signed-off-by: Maros Ondrejicka <maros.ondrejicka@pantheon.tech>
Change-Id: I0e13d9ba1ddcd3ad5835bce1b8cccfc048e5e528
diff --git a/extras/hs-test/vars b/extras/hs-test/vars
index b48793b..3879d57 100644
--- a/extras/hs-test/vars
+++ b/extras/hs-test/vars
@@ -3,4 +3,4 @@
 export HST_LDPRELOAD=${VPP_WS}/build-root/build-vpp_debug-native/vpp/lib/x86_64-linux-gnu/libvcl_ldpreload.so
 export PATH=${VPP_WS}/build-root/build-vpp_debug-native/vpp/bin:$PATH
 
-export UBUNTU_VERSION=22.04
+export UBUNTU_VERSION=$(lsb_release -rs)