Add userdata partition to microdroid

Many programs need /data (especially /data/local/tmp) to properly work.
This change adds a basic unencrypted ext4 userdata partition to
microdroid. Eventually microdroid will support userdata encryption so
only VM can access /data.

Bug: 185767624
Test: atest MicrodroidHostTestCases
Test: log in to microdroid and test writing to /data
Change-Id: I115a8083ad6741fea9dedd61eca7194b1b5e5712
diff --git a/microdroid/init.rc b/microdroid/init.rc
index 61f9ae5..721ba93 100644
--- a/microdroid/init.rc
+++ b/microdroid/init.rc
@@ -78,6 +78,8 @@
     # some services can be started.
     trigger late-fs
 
+    trigger post-fs-data
+
     # Load persist properties and override properties (if enabled) from /data.
     trigger load_persist_props_action
 
@@ -109,6 +111,10 @@
 
     start adbd
 
+on post-fs-data
+    mount_all /vendor/etc/fstab --late
+    restorecon /data
+
 service ueventd /system/bin/ueventd
     class core
     critical