Allow system watchdog to collect traces from vold.

We're investigating a bug where vold gets wedged, and we need to
collect ANR stack traces from it to debug further.

avc: denied { signal } for comm="watchdog" scontext=u:r:system_server:s0 tcontext=u:r:vold:s0 tclass=process permissive=0
avc: denied { ptrace } for scontext=u:r:crash_dump:s0 tcontext=u:r:vold:s0 tclass=process permissive=0

Bug: 122090837
Test: manual
Change-Id: I738e63717715189b9ae2317472f671e3563afaa9

private/crash_dump.te

@@ -15,7 +15,7 @@ allow crash_dump {
   -vold
 }:process { ptrace signal sigchld sigstop sigkill };
 userdebug_or_eng(`
-  allow crash_dump { llkd logd }:process { ptrace signal sigchld sigstop sigkill };
+  allow crash_dump { llkd logd vold }:process { ptrace signal sigchld sigstop sigkill };
 ')
 
 ###
@@ -37,6 +37,7 @@ neverallow crash_dump {
   ueventd
   vendor_init
   vold
+  userdebug_or_eng(`-vold')
 }:process { signal sigstop sigkill };
 
 neverallow crash_dump self:process ptrace;

private/system_server.te

@@ -276,6 +276,7 @@ allow system_server {
   sdcardd
   statsd
   surfaceflinger
+  vold
 
   # This list comes from HAL_INTERFACES_OF_INTEREST in
   # frameworks/base/services/core/java/com/android/server/Watchdog.java.