Allow dumpstate to signal keystore to dump its stack

This is needed to debug hangs in keystore2.

Restricted to debuggable builds for now.

Bug: 186879912
Test: 'adb bugreport', then find the stack traces for keystore2 in the
      "VM TRACES JUST NOW" section of the main bugreport file.
Change-Id: I4434cab7e79cb4aae8bbb2e3a8abff02e0073c13
diff --git a/private/dumpstate.te b/private/dumpstate.te
index 13e3b4c..5b0fd11 100644
--- a/private/dumpstate.te
+++ b/private/dumpstate.te
@@ -53,6 +53,10 @@
   netd
 }:process signal;
 
+userdebug_or_eng(`
+  allow dumpstate keystore:process signal;
+')
+
 # For collecting bugreports.
 allow dumpstate debugfs_wakeup_sources:file r_file_perms;
 allow dumpstate dev_type:blk_file getattr;