Avoid two SELinux related error messages at boot time

It is expected that /metadata/ota/rollback-indicator and /metadata/gsi
don't always exist, so don't call selinux_android_restorecon() on them
when they don't exist.  This eliminates the following error messages:

0     0 E selinux : SELinux: Could not get canonical path for /metadata/ota/rollback-indicator restorecon: No such file or directory.
0     0 E selinux : SELinux:  Could not stat /metadata/gsi: No such file or directory.

Test: Booted Cuttlefish and verified the error messages are gone
Change-Id: I94c998556c85adde5f11f134178219ba7880c2be
diff --git a/init/selinux.cpp b/init/selinux.cpp
index ebdcaa6..ac102eb 100644
--- a/init/selinux.cpp
+++ b/init/selinux.cpp
@@ -735,6 +735,14 @@
     TEMP_FAILURE_RETRY(send(fd.get(), &request, sizeof(request), 0));
 }
 
+int RestoreconIfExists(const char* path, unsigned int flags) {
+    if (access(path, F_OK) != 0 && errno == ENOENT) {
+        // Avoid error message for path that is expected to not always exist.
+        return 0;
+    }
+    return selinux_android_restorecon(path, flags);
+}
+
 }  // namespace
 
 void SelinuxRestoreContext() {
@@ -762,9 +770,9 @@
 
     // adb remount, snapshot-based updates, and DSUs all create files during
     // first-stage init.
-    selinux_android_restorecon(SnapshotManager::GetGlobalRollbackIndicatorPath().c_str(), 0);
-    selinux_android_restorecon("/metadata/gsi", SELINUX_ANDROID_RESTORECON_RECURSE |
-                                                        SELINUX_ANDROID_RESTORECON_SKIP_SEHASH);
+    RestoreconIfExists(SnapshotManager::GetGlobalRollbackIndicatorPath().c_str(), 0);
+    RestoreconIfExists("/metadata/gsi",
+                       SELINUX_ANDROID_RESTORECON_RECURSE | SELINUX_ANDROID_RESTORECON_SKIP_SEHASH);
 }
 
 int SelinuxKlogCallback(int type, const char* fmt, ...) {