Make servicemanager use "bootstrap" bionic

For servicemanager to start in "default" mount namespace before
"apexd", it needs to use "boostrap" bionic.

Bug: 237672865
Test: m && boot
Change-Id: I6551f10f8415ab3ec7cd568321b7db2c3b770807
diff --git a/cmds/servicemanager/Android.bp b/cmds/servicemanager/Android.bp
index 32922ca..3b753c6 100644
--- a/cmds/servicemanager/Android.bp
+++ b/cmds/servicemanager/Android.bp
@@ -44,6 +44,7 @@
     defaults: ["servicemanager_defaults"],
     init_rc: ["servicemanager.rc"],
     srcs: ["main.cpp"],
+    bootstrap: true,
 }
 
 cc_binary {