nixos/osquery: fix database_path + logger_path opts per systemd docs

nixos/osquery: Update tests with option changes

nixos/modules/services/monitoring/osquery.nix

···
           freeformType = attrsOf str;
           options = {
             database_path = lib.mkOption {
-              default = "/var/lib/osquery/osquery.db";
+              default = "osquery/osquery.db";
               readOnly = true;
-              description = "Path used for the database file.";
-              type = path;
+              description = "Path used for the database file, relative to /var/lib/.";
+              type = nonEmptyStr;
             };
             logger_path = lib.mkOption {
-              default = "/var/log/osquery";
+              default = "osquery";
               readOnly = true;
-              description = "Base directory used for logging.";
-              type = path;
+              description = "Base directory used for logging, relative to /var/log/.";
+              type = nonEmptyStr;
             };
             pidfile = lib.mkOption {
               default = "/run/osquery/osqueryd.pid";

nixos/tests/osquery.nix

···
         machine.succeed("echo 'SELECT value FROM osquery_flags WHERE name = \"nullvalue\";' | osqueryi | tee /dev/console | grep -q ${nullvalue}")
 
         # Module creates directories for default database_path and pidfile flag values.
-        machine.succeed("test -d $(dirname ${cfg.flags.database_path})")
+        machine.succeed("test -d $(dirname /var/lib/${cfg.flags.database_path})")
         machine.succeed("test -d $(dirname ${cfg.flags.pidfile})")
       '';
   }