apexd exports its status via sysprop

A sysprop apexd.status is set by apexd, to that other components (i.e.
init) can determine whether APEXs are all successfully mounted or no
(i.e., being mounted).

The sysprop is only writable by apexd.

Bug: 117403679
Test: adb shell getprop apexd.status returns 'ready'.
Change-Id: I81bcb96e6c5cb9d899f29ffa84f91eab3820be25
diff --git a/private/compat/26.0/26.0.ignore.cil b/private/compat/26.0/26.0.ignore.cil
index 1e3977a..1a8c536 100644
--- a/private/compat/26.0/26.0.ignore.cil
+++ b/private/compat/26.0/26.0.ignore.cil
@@ -15,6 +15,7 @@
     apex_service
     apexd
     apexd_exec
+    apexd_prop
     apexd_tmpfs
     atrace
     binder_calls_stats_service
diff --git a/private/compat/27.0/27.0.ignore.cil b/private/compat/27.0/27.0.ignore.cil
index af805df..4e42041 100644
--- a/private/compat/27.0/27.0.ignore.cil
+++ b/private/compat/27.0/27.0.ignore.cil
@@ -14,6 +14,7 @@
     apex_service
     apexd
     apexd_exec
+    apexd_prop
     apexd_tmpfs
     atrace
     binder_calls_stats_service
diff --git a/private/compat/28.0/28.0.ignore.cil b/private/compat/28.0/28.0.ignore.cil
index 6c9fbee..25e95c7 100644
--- a/private/compat/28.0/28.0.ignore.cil
+++ b/private/compat/28.0/28.0.ignore.cil
@@ -14,6 +14,7 @@
     apex_service
     apexd
     apexd_exec
+    apexd_prop
     apexd_tmpfs
     biometric_service
     ;; TODO(b/116344577): remove after the issue is resolved