init: Don't fail first stage mount for formattable partitions.

If a partition can be formatted by vold, then it doesn't make sense to
have first-stage mount fail if the partition hasn't been formatted yet.

Bug: 121209697
Test: device boots after fastboot flashall -w
Change-Id: I4a6c794a9912a5e0794983e9514a08f9c23e6ae9
diff --git a/init/first_stage_mount.cpp b/init/first_stage_mount.cpp
index acefdf0..b5ff658 100644
--- a/init/first_stage_mount.cpp
+++ b/init/first_stage_mount.cpp
@@ -395,6 +395,11 @@
         return false;
     }
     if (fs_mgr_do_mount_one(*fstab_entry)) {
+        if (fstab_entry->fs_mgr_flags.formattable) {
+            PLOG(INFO) << "Failed to mount '" << fstab_entry->mount_point << "', "
+                       << "ignoring mount for formattable partition";
+            return true;
+        }
         PLOG(ERROR) << "Failed to mount '" << fstab_entry->mount_point << "'";
         return false;
     }