lib/sysroot: Add API to get pending/rollback for given stateroot

This imports a function that is used in rpm-ostree, and it's also intended for
use by https://github.com/advancedtelematic/aktualizr to display
what deployment we're going to boot next after the reboot.

Updated-by: Colin Walters <walters@verbum.org>

Closes: #897
Approved by: OYTIS

src/libostree/ostree-sysroot.h

@@ -187,6 +187,12 @@ gboolean ostree_sysroot_deployment_unlock (OstreeSysroot     *self,
                                            GCancellable      *cancellable,
                                            GError           **error);
 
+_OSTREE_PUBLIC
+void ostree_sysroot_query_deployments_for (OstreeSysroot     *self,
+                                           const char        *osname,
+                                           OstreeDeployment  **out_pending,
+                                           OstreeDeployment  **out_rollback);
+
 _OSTREE_PUBLIC
 OstreeDeployment *ostree_sysroot_get_merge_deployment (OstreeSysroot     *self,
                                                        const char        *osname);