MDEV-40403: Add sysuser tools to openSUSE 1600

`sysuser-tools` install the required RPM .attr configuration
files for discovering and processing our generated `sysusers.conf` file.

Without it, RPM isn't able to write the `Provides` user(mysql) / group(mysql)
section to the mariadb-server package metadata, causing the packages
requiring the user to fail installing.

```
Problem: 1: the to be installed MariaDB-server-11.8.8-1.x86_64 requires 'user(mysql)', but this requirement cannot be provided
not installable providers: mariadb-client-11.8.2-160000.2.2.x86_64[openSUSE:repo-oss]
                   mariadb-client-11.8.3-160000.1.1.x86_64[openSUSE:repo-oss]
                   mariadb-client-11.8.5-160000.1.1.x86_64[openSUSE:repo-oss]
                   mariadb-client-11.8.5-160000.2.1.x86_64[openSUSE:repo-oss]
                   mariadb-client-11.8.5-160000.3.1.x86_64[openSUSE:repo-oss]
                   mariadb-client-11.8.6-160000.1.1.x86_64[openSUSE:repo-oss]
                   mariadb-client-11.8.6-160000.2.1.x86_64[openSUSE:repo-oss]
                   mariadb-client-11.8.8-160000.1.1.x86_64[openSUSE:repo-oss]

 Solution 1: do not install MariaDB-server-11.8.8-1.x86_64
 Solution 2: break MariaDB-server-11.8.8-1.x86_64 by ignoring some of its dependencies

Author: RazvanLiviuVarzaru

ci_build_images/opensuse.Dockerfile

@@ -70,6 +70,7 @@ RUN zypper update -y \
     snappy-devel \
     subversion \
     systemd-devel \
+    sysuser-tools \
     unixODBC \
     unixODBC-devel \
     wget \