Adding the ONU bound DHCP detection flows takes > 20 mins for all flows to be added

This issue is being reported for master 1.x using BBSIM simulator
1x OLT and 16x ONUs.
This is related to the execution of the DHCP Test Case execution

Once all subscriber/ONUs reach AUTHORIZED state, the NNI bound DHCP flows are installed in onos

Then proceeding to individually install the ONU bound DHCP flows using the 
`volt-add-subscriber-access` <deviceId> <portNum> command in onos for each results in a severe slowdown in flow establishment in onos

 After waiting for all ONUS to be AUTHORIZED, I then proceed to add the ONU bound DHCP detection flows.
I tried a couple of different ways

1. Add them all at once and then test for the flow presence for each ONU. This causes some sort of long period, > 15 mins where onos indicates a large number of flows in various states of PENDING_ADD, PENDING_REMOVE and some in ADDED state (number of flows > 142) If I leave it for > 20 mins I then see it settle to 132 flows, all in ADDED state
2. Add them each at a time checking to make sure the flows appear before moving on to add the next
   This method takes > 15-20 mins to go through all ONUs

Meanwhile, in each case dhclient begins to request an IP address, and the end result that I see using  dhcpl2relay-allocations is few ONUs having been assigned an IP address, while others are in various DHCP state i.e. DHCPDISCOVERY & DHCPREQUEST without an IP address having been assigned.

There looks to be some sort of very slow interaction between onos and voltha with respect to adding the requested flows.