mkosi: Install various system users/groups in opensuse images

These don't get pulled in automatically and there doesn't seem to
be a "system-users" package so install the ones we need for the
integration tests manually.

mkosi.images/system/mkosi.conf.d/10-opensuse/mkosi.conf

@@ -36,6 +36,11 @@ Packages=
         git-core
         glibc-locale-base
         grep
+        group(bin)
+        group(daemon)
+        group(games)
+        group(nobody)
+        group(root)
         gzip
         iputils
         kernel-kvmsmall
@@ -56,6 +61,11 @@ Packages=
         sed
         shadow
         timezone
+        user(bin)
+        user(daemon)
+        user(games)
+        user(nobody)
+        user(root)
         vim
         xz