init: First Stage Mount observe nofail mount flag

MountPartitions should respect nofail.  The nofail flag makes the
partition optional.

Test: manual (future code using feature), and smoke test
Bug: 109821005
Bug: 78914864
Change-Id: I715a66ef1abbe223b0cefe5bd2758f63352b1afc

init/first_stage_mount.cpp

@@ -375,7 +375,7 @@ bool FirstStageMount::MountPartitions() {
     }
 
     for (auto fstab_rec : mount_fstab_recs_) {
-        if (!MountPartition(fstab_rec)) {
+        if (!MountPartition(fstab_rec) && !fs_mgr_is_nofail(fstab_rec)) {
             return false;
         }
     }