Merge pull request #74 from OpenVoxProject/sles_15_5

build on SLES-15.5 instead of SLES-15.6 for backwards compability

Author: marcusdots

lib/vanagon/platform/defaults/sles-15-x86_64.rb

@@ -22,6 +22,6 @@
   plat.install_build_dependencies_with "zypper -n --no-gpg-checks install -y"
   plat.vmpooler_template "sles-15-x86_64"
   plat.docker_registry "registry.suse.com/suse"
-  plat.docker_image "sle15:15.6"
+  plat.docker_image "sle15:15.5"
   plat.docker_arch "linux/amd64"
 end