Don't start adb if debugging is off

* Debug level None: adb is not supported
* Debug level app_only: adb is supported, but rooting is prohibited
* Debug level full: adb is supported and can be rooted

Bug: 201362865
Test: start a VM with `--debug none` and try to connect to the VM via
adb. It doesn't work as expected.

Change-Id: I95fe01e722d974ff1eb29469ac96abe7d785288d
diff --git a/microdroid/init.rc b/microdroid/init.rc
index 23434bb..078b51d 100644
--- a/microdroid/init.rc
+++ b/microdroid/init.rc
@@ -30,6 +30,8 @@
     # payloads are not designed to run with bootstrap bionic
     setprop apex_config.done true
 
+    setprop ro.debuggable ${ro.boot.microdroid.debuggable:-0}
+
 on init
     # Mount binderfs
     mkdir /dev/binderfs
@@ -80,6 +82,7 @@
     # TODO(b/185767624): remove hidl after full keymint support
     start hwservicemanager
 
+on init && property:ro.boot.adb.enabled=1
     start adbd
 
 on load_persist_props_action