multi: add tor connection healthcheck

This commit adds a new health check, tor connection, to our liveness
monitor. A monitor refactor is applied to the server creation such that
the scope of health check creation is managed within one function.

sample-lnd.conf

@@ -990,6 +990,22 @@ litecoin.node=ltcd
 ; This value must be >= 1m.
 ; healthcheck.tls.interval=1m
 
+; The number of times we should attempt to check our tor connection before
+; gracefully shutting down. Set this value to 0 to disable this health check.
+; healthcheck.torconnection.attempts=3
+
+; The amount of time we allow a call to our tor connection to take before we 
+; fail the attempt. This value must be >= 1s.
+; healthcheck.torconnection.timeout=10s
+
+; The amount of time we should backoff between failed attempts to check tor 
+; connection. This value must be >= 1s.
+; healthcheck.torconnection.backoff=30s
+
+; The amount of time we should wait between tor connection health checks. This
+; value must be >= 1m.
+; healthcheck.torconnection.interval=1m
+
 
 [signrpc]