Don't use qcow2 for userdata.
We provide a sparse file directly as a (writable) partition image and
format a filesystem on the partition inside the VM.
To format it only when it's not formatted, the option `formattable` is
added to the fstab entry for the userdata partition.
Bug: 185767624
Test: atest MicrodroidHostTestCases
Change-Id: Ia938fd60071e64170b8280d19c17c4413c769337
diff --git a/microdroid/fstab b/microdroid/fstab
index 2f4e45f..6e17c3e 100644
--- a/microdroid/fstab
+++ b/microdroid/fstab
@@ -2,4 +2,4 @@
vendor /vendor ext4 noatime,ro,errors=panic wait,first_stage_mount,logical
# TODO(b/185767624): turn on encryption
-/dev/block/by-name/userdata /data ext4 noatime,nosuid,nodev,errors=panic latemount,wait,check
+/dev/block/by-name/userdata /data ext4 noatime,nosuid,nodev,errors=panic latemount,wait,check,formattable