Enable exporting of tombstones out of guest VMs

Microdroid init will start the tombstone_transmit service which will
connect to a server (thread of virtualization service).

virtualizationservice listens for incoming connections from guests VMs.
The client (tombstone_transmit in  guest) sends each tombstone file
content through a separate stream.

For each received connection, handle_tombstone would send a connect
request to tombstoned(via libtombstoned_client_rust), which provide a
file  to write the content in (actually managed by the client libary).
Once write is complete notify_completion() would send completion
notification to tombstoned (which then will close the file and rename it).

Test: atest MicrodroidHostTestCases and/or crash a process in microdroid, take and check bugreport
Bug: 202153827

Change-Id: Ifcaa5da968ef39fdd05612d3e0baca4fd1c5eaf1
diff --git a/microdroid/bootconfig.common b/microdroid/bootconfig.common
index eda95a2..c202ba0 100644
--- a/microdroid/bootconfig.common
+++ b/microdroid/bootconfig.common
@@ -1,2 +1,6 @@
 androidboot.first_stage_console = 1
 androidboot.hardware = microdroid
+
+# tombstone_transmit is enabled. Tombstones will be transmitted to the host
+# TODO(b/227443903) : Make this configurable by VM owners
+androidboot.tombstone_transmit.enabled=1