sqlite: add a hidden --db-backend flag

Add a hidden flag to set the database backend and plumb it into
podman-info.  Further add a system test to make sure the flag and the
info output are working properly.

Note that the test may need to be changed once we settled on how
to test the sqlite backend in CI.

Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

pkg/domain/infra/runtime_libpod.go

@@ -265,6 +265,10 @@ func getRuntime(ctx context.Context, fs *flag.FlagSet, opts *engineOpts) (*libpo
 		options = append(options, libpod.WithRegistriesConf(cfg.RegistriesConf))
 	}
 
+	if fs.Changed("db-backend") {
+		options = append(options, libpod.WithDatabaseBackend(cfg.ContainersConf.Engine.DBBackend))
+	}
+
 	// no need to handle the error, it will return false anyway
 	if syslog, _ := fs.GetBool("syslog"); syslog {
 		options = append(options, libpod.WithSyslog())