Add MQTT specs. etc/vm.args: -env ERL_CRASH_DUMP log/emqttd_crash.dump

rel/files/vm.args

@@ -58,3 +58,4 @@
 ## Tweak GC to run more often
 -env ERL_FULLSWEEP_AFTER 1000
 
+-env ERL_CRASH_DUMP log/emqttd_crash.dump