CORDA-1628: Increase max restart count for notary client flows. (#3357)

This will ensure that the notary client flow will retry over a sufficient
period of time for the notary to update its network map.

With a backoff base of 1.8 and 5 retries the last retry will fire after
about 20 min 8 sec of the initial flow start:

#   Timeout, sec
0	30
1	54
2	97.2
3	174.96
4	314.928
5	566.8704

Total 1207.9584	= 20.13264 min

node/src/main/resources/reference.conf

@@ -22,6 +22,6 @@ rpcSettings = {
 }
 flowTimeout {
     timeout = 30 seconds
-    maxRestartCount = 3
-    backoffBase = 2.0
+    maxRestartCount = 5
+    backoffBase = 1.8
 }